Sen. John McCain (R-Ariz.) asked former FBI director James Comey a series of questions at a Senate Intelligence Hearing, but appeared to be confused about FBI investigations, on June 8 at the Capitol. (Reuters)

Sen. John McCain (R-Ariz.) was the last senator to question former FBI director James B. Comey at Thursday's dramatic Senate Intelligence Committee hearing. Nearing the end of more than 2½ hours of questioning, McCain focused his line of questioning on two FBI investigations: the 2016 investigation into Hillary Clinton's use of a private email server and the 2017 investigation into Russian interference in the presidential election.

But several of his questions confused viewers, and seemingly Comey himself, and occasionally became incoherent. He referred to “President Comey,” and at times looked confused and frustrated with Comey's answers.

“In the case of Hillary Clinton, you made the statement that there wasn't sufficient evidence to bring a suit against her, although it had been very careless in their behavior, but you did reach a conclusion in that case that it was not necessary to further pursue her,” McCain's line of questioning began. “Yet at the same time, in the case of Mr. (Trump), you said that there was not enough information to make a conclusion. Tell me the difference between your conclusion as far as former Secretary Clinton is concerned, and Mr. Trump.”

Comey answered that the Clinton email investigation was a completed, closed investigation at the time he announced that “no reasonable prosecutor” would bring a case against her last July, while the Russia investigation is still underway and could be for some time.

But McCain wasn't satisfied. He seemed to be arguing that Comey exonerated Clinton, in a sense, but left an investigation looming over President Trump, setting a double standard.

Comey again tried to explain that he only discussed the findings of the Clinton investigation after it was completed.

“That investigation was going on. This investigation was going on. You reached separate conclusions,” McCain asserted. Comey explained, for the third time, that the Clinton investigation was about an email server and was concluded in July 2016.

That's when it got really weird.

“You're gonna have to help me out here,” McCain said. Comey replied that he was confused. In the video above, you can watch the entire exchange. But it boiled down to one point.

“I think it's hard to reconcile, in one case you reach a complete conclusion, and on the other side you have not,” McCain said. “I think that's a double standard there, to tell you the truth.”

Well, of course. The Clinton email investigation ended more than 11 months ago, while the Russia investigation continues. It was a bizarre argument from McCain, who appeared visibly annoyed with Comey. Was he arguing that Comey should publicly exonerate President Trump before the Russia investigation is finished? Was he arguing that Comey didn't investigate Clinton vigorously enough? Was he arguing that the FBI applied different standards to the two candidates?

It's hard to say, but McCain seemed to be trying to blunt the effect of Comey's testimony about President Trump.

That's made all the more bizarre by the fact that, since Election Day (and even going back to the 2016 campaign), McCain has been one of the Senate Republicans most critical of Trump and his administration.

Sen. John McCain (R-Ariz.) has repeatedly come under attack from President Trump. Here are just a few of their rocky moments. (Peter Stevenson/The Washington Post)