Senate Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) engaged in a heated hour-long exchange over filibuster rules on the Senate floor Thursday, and by the end of the day, McConnell said Reid risked becoming the worst Senate leader in history.

If Reid goes through with the so-called nuclear option, McConnell said, "our friend the majority leader is going to be remembered as the worst leader here ever."

It wasn't the first allusion to Reid ruining his legacy. Thursday morning, McConnell quoted Reid's previous opposition to filibuster rule changes from when Reid was in the minority in 2005, and suggested making them now would be on his political tombstone.

"'Breaking the rules to change the rules is un-American' – his words, not mine," McConnell said. "I just hope the majority leader thinks about his legacy, the future of his party and, most importantly, the future of our country before he acts."

The two went back and forth for about an hour, with both referring to each other's past comments on filibuster changes.

Reid said that such changes should only be made in extraordinary circumstances -- and argued that the current Republican obstructionism of nominees represents just such a circumstance. Reid is only seeking to change filibuster rules on Cabinet and agency nominations -- not for all Senate business.

"It could be said Sen. McConnell broke his word," Reid said, referring to McConnell pledging to allow votes on nominees through regular order of the Senate. "The Republican leader has failed to live up to his commitments. He has failed to do what he said he would do, move nominations by regular order except in extraordinary circumstances. I refuse to unilaterally surrender my right to respond to this breach of faith."

By Thursday afternoon, McConnell's staff tweeted an image suggesting the move would be on Reid's tombstone: