US President Barack Obama speaks before designating 346,177 acres (140,093 hectares) of national forest land in the San Gabriel Mountains as a national monument during a speech at Frank G. Bonelli Regional Park in San Dimas, California, October 10, 2014. AFP PHOTO / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)

WASHINGTON -- One of the most unpredictable outcomes of a GOP takeover of the Senate, which is looking likely, is the fate of President Barack Obama's judicial nominees.

Republicans, who have been systematically delaying action on nominees all year, would have the ability to block any of Obama's judicial picks in his final two years in office. As the majority, they would control when, or if, his nominees get voted out of the Judiciary Committee and whether they get confirmed on the floor.

There's plenty of residual anger among Republicans over Democrats changing filibuster rules last year, and that anger could well translate into payback. In response to GOP obstruction of Obama's D.C. Circuit Court nominees, Democrats changed the Senate rules last fall so it only takes a simple majority, instead of 60 votes, to advance most nominees. The effect has been Democrats confirming piles of Obama's judicial nominees, with Republicans fuming about being cut out of the process.

Republicans have so far retaliated by using procedural maneuvers to delay votes on nearly every nominee. But they've also warned that Democrats will rue their decision once they end up in the minority.

"I say to my friends on the other side of the aisle, you’ll regret this," Senate Minority Leader Mitch McConnell (R-Ky.) said as Democrats pushed through the change in rules. "And you may regret it a lot sooner than you think."

It's unclear whether McConnell would keep the change in place if he became majority leader, but that doesn't matter much while Obama is in office. The real question for the next two years is whether Republicans would be willing to play ball with the White House in agreeing to judicial nominees. And if the GOP controls the Senate, for the first time under Obama, it would have real leverage.

"If Republicans control the committee and the floor, it makes sense for a Democrat president to meet them in the middle," said a Senate GOP leadership aide. "This is something that [Sen. Chuck Schumer (D-N.Y.)] demanded for a Republican president with a Democrat majority."

Some observers are already predicting a nominations crisis if Republicans win the Senate. Norm Ornstein, a scholar with the American Enterprise Institute, said he expects approximately zero judges would get confirmed for the rest of Obama's term.

The White House doesn't view the situation as quite so dire.

Neil Eggleston, the president's counsel and point person for advancing judicial nominations, says he's got a great working relationship with Republicans, and that in the event that they win control of the Senate, he doesn't expect a standstill on nominations. Even now, he said, there are productive talks underway with Republicans to line up nominees for empty court seats.

"I predict a lot of progress between now and the lame duck," Eggleston told The Huffington Post last month.

The biggest challenge for Obama is getting Republican senators to put forward nominees that he can support. There are currently 16 vacancies without nominees in states with two GOP senators, according to Alliance For Justice data, compared to eight vacancies without nominees in states with one GOP and one Democratic senator. There are just four vacancies without nominees in states with two Democratic senators.

Nominees must be signed off on by the White House and home-state senators, so it's not surprising that states with two Republican senators have the most vacancies without nominees. In some cases, senators may not like Obama's proposed picks, or vice versa. In other cases, senators may be trying to hold off on filling empty court seats until a Republican is in the White House. These are lifetime appointments, after all.

But the White House has struck some significant nominations deals with Republicans this year, in spite of the polarized climate on Capitol Hill. The Senate confirmed several nominees to fill emergency judicial vacancies in Arizona, which has two Republican senators, and in Florida, which has one. Just last month, Obama nominated seven district court nominees in states including Texas, North Carolina and Utah -- all states with at least one GOP senator.

One strategy the White House has used with Republicans -- and one that may become more common if the GOP wins the Senate -- is cutting a deal on a package of nominees that includes some Republican picks and some Democratic picks. That approach worked for advancing Pennsylvania nominees, and has mostly worked for advancing Georgia nominees. Democrats appear to have torpedoed one nominee in the Georgia package, Michael Boggs,, but the other nominees have moved forward.

Notably, the White House continues to defend Boggs against Democratic critics, a sign to other Republican senators that Obama will uphold whatever deals he cuts on nominees.

Of course, if Democrats keep the Senate, the president still faces obstacles. Obama would be able to move his judicial picks more quickly through the process, but he needs Republicans to work with him more than ever to come up with new nominees. Democrats cleared so many judicial nominees in the last year that the Senate practically ran out of people to confirm.

In total, the president is tasked with filling 60 district and circuit court vacancies.

Regardless of whether they keep their majority, Democratic leaders are planning a big push on judicial nominations in the lame duck session. Sixteen district court nominees are currently waiting for a floor vote, and 18 are waiting for a committee vote (though one of those is Boggs). Nominations that don't get confirmed in the lame duck will expire and be returned to the president at the end of the year.