WASHINGTON — Against the backdrop of a looming Supreme Court fight, a less visible battle in the judicial wars is playing out over a conservative Western Pennsylvania attorney and charges of Republican strong-arming.

Senate Republicans are poised on Thursday to break with tradition and advance the nomination of David Porter, an attorney chosen by President Trump for a seat on the Third Circuit Court of Appeals, which oversees cases in Pennsylvania, New Jersey, Delaware, and the Virgin Islands.

They are expected to do so despite objections from Sen. Bob Casey (D., Pa.), who had moved to block Porter using a decades-old Senate custom — known as the blue slip — that gives lawmakers in either party the prerogative to reject judicial  appointments from their home state.

It was a change from the GOP leadership's behavior in 2016, when Pennsylvania's Republican senator, Pat Toomey, used the same privilege to stop one of President Barack Obama's nominees to the same circuit.

Porter, though, has received a hearing from the Senate Judiciary Committee and is scheduled for a committee vote this week.

The move is one more escalation in the decades-long fight over federal courts, one in which both parties have thrown out old standards meant to force compromise and pushed tensions to the boiling point now seen in the Supreme Court battle.

"The other word you can use is hypocrisy," said Russell Wheeler, who studies judicial nominations as a visiting fellow at the Brookings Institution. "The Republicans, they really weaponized that blue slip under Obama."

At stake are lifetime seats on courts that can have vast influence over U.S. laws, and that often serve as stepping stones for future Supreme Court justices.

Though not written into law, the custom of getting sign-off from home state senators — on blue pieces of paper — forces consultation between the White House and the chamber, and fosters a measure of bipartisanship in states, like Pennsylvania, with senators of both parties. Traditionalists say it helps weed out extreme nominees.

While there have been some rare exceptions, both parties have largely honored the practice, and both strictly enforced it during the Obama and George W. Bush presidencies.

No Obama judicial nominees were confirmed by the Senate while still having blue-slip problems — even when Democrats controlled the chamber, according to the non-partisan Congressional Research Service. In all, 18 Obama picks were blocked. Under Bush, 22 were stifled due to such objections.

Republican Senate leaders, however, are poised to make Porter the fourth Trump circuit court nominee to advance through the judiciary committee over the objections of one or both home state senators, said Carl Tobias, a University of Richmond law professor who tracks judicial nominations. Two have been confirmed by the full Senate and seated on the bench, and a third is awaiting a full Senate vote.

"The contrast is pretty striking," Tobias said. "The Republicans took advantage of it, and now they're singing a different tune."

The judiciary committee chairman, Sen. Chuck Grassley (R., Iowa), argued Thursday that individual senators shouldn't be able to block circuit court nominees — who oversee cases in multiple states — if the senators were consulted by the White House before the nomination.

He said the White House told Casey it was considering Porter more than a year before it happened, and suggested several other nominees, but the Democrat rejected them all.

"Because the White House did reach out, we're moving forward with the nomination," Grassley said at a hearing.

"The White House is lying," a Casey spokeswoman shot back in an email. "No one should be surprised that an Administration, which lies with pathological zeal about everything from crowd sizes to basic statistics, would make false representations about the judicial nomination process."

She said Casey has "a bipartisan record" on judges. The senator allowed a previous Trump circuit court choice, Stephanos Bibas, to advance and last week he praised two Trump nominees for Pennsylvania district courts — though he also rejected the president's Supreme Court nominee, Brett Kavanaugh, before he was even nominated.

Casey has signaled since last year that he would oppose Porter, who has drawn the ire of Pennsylvania liberals.

In 2016, Grassley honored Toomey's objection to Rebecca Ross Haywood when Obama nominated her to the Third Circuit. Toomey said then he had made his reservations clear to Obama. The fight came amid another tense moment over the Supreme Court, as Republicans blockaded Obama's nominee, Merrick Garland from even getting a hearing.

Democrats' top senator on the judiciary committee, Dianne Feinstein, warned Grassley over his decision to override Casey on the Porter appointment.

"We all must remember what goes around comes around," Feinstein, of California, said last week. Overriding home state senators, she said, is not "in the best interest of congeniality."

Casey has said Porter's ideology would "serve only the wealthy and powerful."

Toomey has praised the nominee as "one of the preeminent attorneys in Western Pennsylvania," and defended Republicans' push to advance him.

"Neither party has given the other party a complete veto power over circuit court nominees," Toomey said in an interview.

Asked about his own block on an Obama nominee, Toomey said that if Democrats had controlled the Senate then, "I think that would have been a different story."

Democrats in 2013 had used their majority to weaken the Senate filibuster rules, allowing them to approve most judicial nominees without support from Republicans, his aides noted. Republicans followed by ending the filibuster for Supreme Court nominees when they gained power in 2017.

Wheeler, however, noted that Democrats did honor Republican blue slip objections when they most recently held the majority.

While chairmen in both parties have allowed occasional breaks with the blue slip tradition in the past, according to the Congressional Research Service, those are rare exceptions. Under Bush and Obama, judicial nominees who faced home-state objections did not move forward unless the concerns were dropped.

The erosion of the tradition now, with GOP control of Congress and the White House, means there is one less incentive for consensus, Wheeler said.

"The Republicans are doing things realizing full well (that) when the Democrats take over they're going to up the ante even more," he said. "The blue slip thing is part of a larger panorama of the continued degradation of a process."