We count at least three Senate Republicans who have floated the idea of blocking a President Hillary Clinton's Supreme Court nominee indefinitely. Legally, they totally can do it. Politically, it could backfire.

That's because most Senate Republicans' reason for blocking President Obama's nominee was predicated on a timeline (Nov. 8) and a person: the next president.

Hours after Justice Antonin Scalia unexpectedly died in February, Senate Republicans' leader, Sen. Mitch McConnell (R-Ky.), announced that the Senate would wait until the next president took office to fill this vacancy. It's only fair to the American people to let them have a say in this momentous decision, he argued. (Besides, you know, the 2012 election.) A majority of Senate Republicans parroted McConnell's "wait until after the election" argument.

Republicans were gambling they'd win the White House and be able to replace a conservative justice with another conservative. Now that they might be on the brink of losing (both the gamble and the White House), the ones advocating yet another blockade will have some tricky explaining to do about why this one is necessary. Besides, you know -- the obvious.

Sens. John McCain (Ariz.), Ted Cruz (Texas) and Richard Burr (N.C.) have all said in the past few weeks they'd consider not considering Clinton's pick and leaving the 9th seat on the court open indefinitely. McCain even promised to take that path, though he walked back that pledge a day later. (There's a way for Republicans to block Clinton's nominee whether they stay in the majority or are in the minority.)

Other GOP senators, like John Cornyn (Texas) -- the Senate's No. 2 -- and Marco Rubio (Fla.) are dodging the question but have left open the possibility of a blockade. (Rubio says he opposes the idea of a blockade in principle, but again left the possibility open to block a nominee he doesn't agree with.)

President Obama criticizes Republicans who have suggested blocking President Hillary Clinton's Supreme Court nominee indefinitely. (The Washington Post)

There's no line in the Constitution that says the Senate has to confirm a president's Supreme Court appointee, says Russell Wheeler, a Supreme Court expert with the Brookings Institution. But there could be political repercussions when these Senate Republicans try to explain why they said the next president should get to decide, but now...don't want to let the next president decide.

Here's McCain's statement after Obama nominated federal Judge Merrick Garland in March.

"This issue is not about any single nominee – it’s about the integrity of the Court. With less than a year left in a lame-duck presidency and the long-term ideological balance of the Supreme Court at stake, I believe the American people must have a voice in the direction of the Supreme Court by electing a new president. The last time the American people spoke, they elected a Republican majority to the Senate to act as a ‘check and balance’ on President Obama’s liberal agenda – a responsibility I cannot ignore. We must allow the people to play a role in selecting the next lifetime appointment to the Supreme Court.”

(Bold emphasis added by me.)

Here's Cruz: “I proudly stand with my Republican colleagues in our shared belief – our advice and consent – that we should not vote on any nominee until the next president is sworn into office. The People will decide."

Here's Burr:

Here's Cornyn: “At this critical juncture in our nation's history, Texans and the American people deserve to have a say in the selection of the next lifetime appointment to the Supreme Court... The only way to empower the American people and ensure they have a voice is for the next president to make the nomination to fill this vacancy.”

In a February presidential debate, Rubio said he didn't think Obama should appoint someone and that it wouldn't be the worst thing in the world to wait until after the election: "I do not believe the president should appoint someone, and it’s not unprecedented."

The irony is that so far, Senate Republicans have been able to get away with setting a record for longest Supreme Court vacancy. Republicans might lose control of the Senate, but it won't be because of Garland, who is not top of mind for most American voters despite Senate Democrats' attempts to make it so.

But another blockade could make it top of voters' minds.

Democrats have a real case to make now that some Republicans are trying to go back on their word: We waited until after the election, like you wanted. We let the American people pick a new president, like you wanted. Now, why aren't you considering the new president's nominee?

That line of attack lays bare just how politically motivated this whole debate about the ninth Supreme Court justice is (and to be clear, it's political on BOTH sides of the aisle). If there's one thing we've re-learned this election cycle, it's that American voters really, really don't like a politician who comes across as politically calculating. And without a good legal or constitutional explanation about why another blockade is necessary, Republicans risk coming across as very politically calculating.

And what happens if, at some point in Clinton's presidency, another vacancy opens? Or the court splits 4-4 or passes on some big cases that grab the spotlight? Democrats could pin the blame squarely on Republicans.

To sum up, Senate Republicans certainly could decide to block a Clinton pick. But they'll have to talk themselves out of a tight corner to do it.