Senate Majority Leader Mitch McConnell (R-Ky.) will likely go down in history for firming up this precedent about a Supreme Court vacancy in an election year: It’s okay to leave it open until after the election.

But now that it could benefit his party to fill Supreme Court vacancies in an election year, he’s signaling he’s open to setting that precedent aside. And, to justify doing so, he’s pulling out a rationale he made back in 2016, when he held up President Barack Obama’s pick for a Supreme Court opening for more than a year.

McConnell told reporters Monday that if he had a chance to help President Trump fill Supreme Court vacancy in 2020, he’d try to do it. His reasoning is that now that the Senate and the White House are the same party, it’s okay to move on election-year appointments.

“The tradition going back to the 1880s has been if a vacancy occurs in a presidential election year, and there is a different party in control of the Senate than the presidency, it is not filled,” McConnell said.

"Look, it's practical,” he added. “Think about it. There’s no chance that an opposition party in control of the Senate is going to fill a Supreme Court vacancy occurring in the middle of a presidential election year, and that’s why it hasn’t happened since the 1880s."

The Senate can’t even agree when its own filibuster rules should apply. (JM Rieger/The Washington Post)

McConnell isn’t wrong that the Senate of one party rarely confirms an opposing president’s Supreme Court nominee in an election year. As he said, that’s partly a function of politics: Why would you, if you’re the Senate leader, give the other side a win just before an election? But it’s also a function of how rarely the stars align to have all three situations: 1) a Senate of one party, 2) a White House of another and 3) a Supreme Court vacancy in an election year.

A Fix analysis found that there have been just 13 election-year Supreme Court vacancies since 1800. Six of those were filled the same year.

But back in 2016, McConnell wasn’t parading around that argument as his main point for holding up Obama’s nomination of Merrick Garland. He was championing a decidedly less political one: that an outgoing president shouldn’t get to decide a lifetime appointment to the Supreme Court.

“The American people‎ should have a voice in the selection of their next Supreme Court Justice,” McConnell said in a statement hours after Justice Antonin Scalia’s death in February 2016. “Therefore, this vacancy should not be filled until we have a new president.”

McConnell did say once or twice in 2016 that Republicans shouldn’t be expected to approve Obama’s nominee in an election year because they are Republicans and Obama isn’t.

“You’d have to go all the way back to 1888 with Grover Cleveland, a Democrat in the White House, to find the last time a Senate of the opposite party confirmed a nominee to a vacancy on the Supreme Court occurring in a presidential year,” he said in 2016 on the Hugh Hewitt radio program.

In a letter that Republicans on the Senate Judiciary Committee sent to McConnell arguing to hold up Obama’s pick, they also brought up how rare it would be for Republicans to confirm a Democratic nominee in that case: “It is necessary to go even further back — to 1888 — to find an election-year nominee who was nominated and confirmed under divided government, as we have now,” they wrote.

But that wasn’t an argument they made frequently. The average person listening to McConnell and Senate Republicans heard them focus on the outgoing president’s status rather than his party.

“Given that we are in the midst of the presidential election process, we believe that the American people should seize the opportunity to weigh in on whom they trust to nominate the next person for a lifetime appointment to the Supreme Court,” McConnell and Senate Judiciary Chairman Charles E. Grassley (R-Iowa) wrote in a Washington Post op-ed at the time.

McConnell said things in that vein over and over again in 2016, and it was effective. His gamble to hold the seat open for a Republican president to fill paid off. But the problem he has now is how to square what he said back then now that he wants to confirm Supreme Court justices in an election year.

With two of the court’s more liberal justices over 80 years old, there’s a chance in 2020 that McConnell could face the same situation he in 2016: still in control of the Senate, with an outgoing president and a Supreme Court vacancy they would confirm. The only difference would be that Republicans control both the Senate and the White House.

Hence, McConnell is seizing on an argument that isn’t the primary one he made two years ago.

None of this to say McConnell is breaking any rules on election-year appointments. That’s because there are no rules. If Republicans keep control of the Senate this November, they’ll have the authority to confirm (or not confirm) a president’s Supreme Court pick.

Plus, it’s impractical to expect McConnell to hold off on confirming a Supreme Court pick from his own party, one that could very likely thrust the court much more conservative.

"Frankly, it would be shocking for a majority leader of either party in McConnell’s position to rule out confirming a justice in a situation like that,” said Josh Chafetz, a Cornell University law professor and expert on the nexus of Congress and the Supreme Court.

In bringing up how opposing parties generally don’t cooperate with presidents on Supreme Court vacancies in an election year, McConnell left himself wiggle room in 2016 for this moment in 2020. But in using that wiggle room, it sounds to many like he’s flip-flopping because it’s politically convenient for him.

J.M. Rieger contributed to this report.