Could Senate Minority Leader Mitch McConnell, R-Ky., possibly lose his primary?

Sen. John McCain, R-Ariz., thinks he faces a "tough" battle, made tougher by his vote to break a filibuster of the debt limit increase.

“I must say that it was a very courageous act, especially Sen. McConnell, who -- as you well know -- is in a very tough race," McCain told Politico on Wednesday, in an apparent allusion to the fact that the vote gives his primary challenger, Matt Bevin, political ammunition against McConnell.

Sixty-seven senators voted to end debate on the debt limit increase, though McConnell and the rest of the Senate Republicans voted against the debt limit increase itself.

Sen. Lindsey Graham, R-S.C., also seems to believe that McConnell took a risk by voting to end debate. "Hopefully the other people voting with him helps, and hopefully people see it as an act of pragmatic leadership," Graham told The Hill.

Both Graham and McCain said their Kentucky colleague was put in a corner by House Republicans. "I think people understood that he is not for raising the debt ceiling without something attached; obviously that was impossible after the House voted for a clean increase," Graham said. (Politico said McCain initially voted against ending debate, but changed his vote after McConnell voted in favor.)

Graham and McCain are hardly darlings of the Republican base, but Sen. Mike Lee, R-Utah, a Tea Party favorite, also put the blame on House Republicans, telling constituents in a Wednesday evening tele-town hall that he was "very disappointed" the House sent a clean debt limit increase over to the Senate.

"This is wrong and this is exactly how we got to the point where we're now 17-plus trillion dollars in debt," said Lee, who voted "no" on ending debate and on raising the debt ceiling. "It was an unfortunate step that the House of Representatives took yesterday [and] it was an unfortunate step that the Senate took today when it passed that same measure."

Another takeaway from Wednesday's vote: If this vote to end debate does cause McConnell a problem with the conservative base, then Sen. Ted Cruz, R-Texas, just made him walk the plank.

“It should have been a very easy vote,” Cruz told Politico. “In my view, every Senate Republican should have stood together and said what every one of us tells our constituents back home, which is that we will not go along with raising the debt ceiling while doing nothing to fix the underlying out-of-control spending problem.”

It remains to be seen if Bevin can pull the primary upset. Politico obtained a financial report signed by Bevin when he was president of Veracity Funds that praised the 2008 bailouts, which Bevin has used to attack McConnell during this campaign. Bevin explained to Glenn Beck that he didn't actually write the letter.

"I did not write any of the letters that were ever published as investment commentary for Veracity Funds," he said Tuesday. "I was the president and chairman of the board and by [Security and Exchange Commission] law, was required to sign prospectuses when they were sent out."

That said, Bevin did criticize the Cruz and Lee's attempt to defund Obamacare, which failed after a 16-day government shutdown.

“We have way too much partisanship in Washington,” Bevin said in January. “And it shouldn't be a function of, you know, the Democrats are this, therefore the Republicans have to be opposed to it or vice versa. It's got to be what's in the best interest of this country. Shutting down the government is ridiculous.”

As of December, Bevin wasn't connecting with primary voters, most of whom didn't know him. "And the voters who do have an opinion about him don't particularly like him — just 14 percent see him favorably to 25 percent with a negative opinion," according to Public Policy Polling, a Democratic-leaning firm. "GOP voters say they like Rand Paul better than McConnell by a 59/27 margin, but so far they're not seeing Bevin as someone in the Paul vein."

His comments about the shutdown didn't alienate the Senate Conservatives Fund, even though the group supported Cruz and Lee through that fight. The group just released an anti-McConnell ad that stands as its "harshest attack yet," as the Washington Examiner's Byron York put it Wednesday, "based in part on supposition, misleading reporting, questionable assertions and a single (erroneously cited) poll."