When the united states senate returned to work in early september after its summer recess, it faced a daunting in-tray. the nations coronavirus death toll has exceeded 1,000 people on several days this month and many of the emergency economic measures to deal with the crisis have expired.

But with the parties divided over new economic stimulus, senate republicans have continued instead with the quiet task that has preoccupied them for much of donald trumps presidency: placing young and reliably conservative judges on the federal courts.

More than a dozen district judges have been installed into lifetime positions in september alone, part of mr trumps near-record first-term tally of 217 judicial appointments.

On saturday, the president is expected to nominate a successor to ruth bader ginsburg, the liberal supreme court justice and only the second woman to ever serve on the high court, who died on september 18. if confirmed by the senate as is expected, this would be his third appointment to the supreme court, tilting it firmly into the hands of conservatives who will have a 6-3 majority.

But even absent that decisive victory, mr trumps four years in office have allowed republican lawmakers to dramatically reshape the us judicial system by installing rightwing judges at a pace almost unmatched in american history.

Mr trumps judges, carefully selected for their ideological bona fides, have already begun to reshape us law in a more conservative direction on issues as wide ranging as gun control, voting rights, environmental protections, abortion and immigration.

One upshot could be a scenario where a future congress controlled by the democrats passes legislation on climate change or healthcare, only for conservative judges to throw out those laws on the grounds of government over-reach.

The disciplined operation for nominating judges is one of the main reasons republicans in congress have given mr trump such loyal support even amid the chaotic response to the pandemic.

Today, almost a third of all active federal judges on the us appeals courts were appointed by mr trump. at the district court level, the front line for civil and criminal cases, mitch mcconnell, the senate majority leader, has continued to confirm mr trumps appointees at a rapid clip.

Leave no vacancy behind, mr mcconnell said earlier this year.

Mike davis, a former top republican senate judiciary staffer who helped confirm many of the presidents judicial appointees, says mr trump campaigned in 2016 on a promise to transform the federal judiciary with conservative judges.

President trump has absolutely delivered on that promise, he says. it is the most significant achievement of his first term.

For the vast majority of people and companies who appear in federal court, the three-judge panels that hear appeals from district courts are the final arbiters in their cases. few cases are reheard en banc or by all of the judges on each of the 13 courts of appeals known as circuit courts and fewer still make their way up to the supreme court.

The impact of mr trumps appointments is being felt most keenly on these key appeals courts, which republicans have prioritised. those randomly-selected three judge panels that determine the vast majority of appeals are now increasingly likely to have at least two conservatives interpreting the law.

The ninth circuit court of appeals, which covers cases heard in california and other western states, was once a liberal bastion. under mr trump, its previous 11-strong majority of democrat-appointed judges has been whittled down to just three.

In august, a three-judge panel on the ninth circuit, in a 2-1 split decision, struck down a california gun control law that outlawed weapons with high-capacity magazines. the judge writing for the majority, kenneth lee, was appointed by mr trump in 2019.

Armed self-defence is a fundamental right rooted in tradition and the text of the second amendment, mr lee wrote in his opinion. californias attorney-general, xaxier becerra, has asked the ninth circuit to rehear the case en banc.

Elsewhere, mr trumps appointees have bolstered republican majorities on four of the 13 appeals courts, and flipped three from majority democrat-appointed to majority republican-appointed.

Among the courts that have flipped is the eleventh circuit court of appeals, which includes florida. in 2018, voters in the state changed the florida constitution to grant former convicts the right to vote. republican state legislators subsequently limited the change to only those who had paid off outstanding fines.

This month, the 11th circuit upheld the move by the republican legislators in a 6-4 en-banc decision. all but one of the judges in the majority were appointees of mr trump among them barbara lagoa, one of the front-runners for ginsburgs seat on the supreme court.

The dizzying pace with which the republican party machinery has engineered this shift only democratic president jimmy carter, under whom the courts were expanded to cope with a greater workload, beats mr trump on first-term judicial appointments has shaken liberals.

They have really done a number on transforming the courts, says lena zwarensteyn, a campaign director at the leadership conference on civil and human rights. there is a lot of damage that has to be repaired.

For mr trump, it is a key part of his pitch to conservative voters as he seeks re-election this year against joe biden. hundreds of federal judges would need to be chosen over the next four years, he said earlier this month. the outcome of these decisions will determine whether we hold fast to our nations founding principles or whether they are lost forever, he added.

The transformation of the federal courts under mr trump has its origins in the presidency of barack obama.

Until 2013, senate rules meant 60 votes were required to confirm appeals court judges. harry reid, then the democratic majority leader, changed the threshold to a simple majority, citing obstruction of mr obamas nominees by republicans led by mr mcconnell. after republicans took back the senate in 2015, the confirmations ground to a near halt.

Only two appeals court judges nominated by mr obama were confirmed by the senate when republicans controlled the chamber. in his entire eight years in office, mr obama managed 55 appeals court appointments only two more than mr trump has achieved in half the time.

The strategy deployed by mr mcconnell would ultimately reach its zenith in his refusal to allow even hearings let alone a vote on merrick garland, mr obamas nominee to fill the supreme court vacancy left by the death of antonin scalia in 2016.

The result was a raft of vacancies waiting to be filled when mr trump took office. his first confirmed appeals court judge, amul thapar, took up a seat on the sixth circuit in 2017 that had been empty for four years.

Unlike the democrats before them, republicans under mr trump have moved with a single-minded focus to fill court vacancies, particularly in the appeals courts.

Don mcgahn, who was mr trumps first white house counsel, centralised control of the vetting and nominations process in his office. too many cooks in the kitchen makes for a bad meal, he said in a speech last year.

Most of the appeals court judges selected had ties to the federalist society, the conservative and libertarian legal group, the new york times reported in march. they have skewed white and male, and more ideologically hardline than those picked by previous republican presidents.

Previous republican presidents may have talked about shrinking the size of government, mr mcgahn said in his 2019 speech, given at a federalist society conference in philadelphia, but they tended to pick judges...who were very deferential to those wielding governmental power.

He added: generally speaking, we did not.

Democrats have been all but powerless to stop the conveyor belt of judicial appointments these past four years. the remarkable success of this project has altered the political dynamics around judicial appointments, at least to the appeals courts.

What was once a process that included some limited bipartisan agreement is now a game of a hardball where the party that controls the senate confirms nominees from its own president, and blocks the nominees of the opposing party.

If and when democrats retake the senate, theyll say its time to pay the piper, says russell wheeler, a brookings institution fellow who studies judicial nominations.

Christopher kang, who worked in the obama white house on judicial nominations and is now chief counsel at advocacy group demand justice, says the republicans had instituted a new playbook on appointing judges. democrats will follow that playbook next time theyre in power, he says.

Some democrats are talking openly about the need to expand the supreme court to dilute the impact of mr trumps appointments. mr kang says the party should go even further and increase the size of appeals courts.

Were going to have to be more aggressive in how we seek to restore balance, he says.

Those arguments reflect the bigger question posed by mr trumps judicial appointments, whether they will significantly constrain the ability of democratic politicians to implement laws that are opposed by conservatives, like stricter election regulation, gun controls or expanded healthcare.

Even if mr trump serves only one term, and republicans lose the senate in november, the judges installed these past four years look set to serve as a bulwark of conservative power.

Republicans understand that the federal judiciary is the last line of defence against government over-reach and mob rule, says mr davis, the former republican senate judiciary staffer who now runs a judicial advocacy group, the article 3 project.

Some see risks in the political warfare over control of the courts. ian bassin, a former associate white house counsel in the obama administration, says that an independent and trusted judiciary is a linchpin of healthy, functioning democracies.

History is replete with examples of countries that either never gained that or lost it because they allowed raw power grabs to capture and corrupt courts, says mr bassin, who now runs a group called protect democracy. once one side does it, the other side responds in kind and the death spiral begins.