Sen. Al FrankenAlan (Al) Stuart FrankenTake Trump literally and seriously in Minnesota Ninth woman accuses Al Franken of inappropriate contact Al Franken to host SiriusXM radio show MORE (D-Minn.) says Donald TrumpDonald John TrumpBusiness school deans call for lifting country-specific visa caps Bolton told ex-Trump aide to call White House lawyers about Ukraine pressure campaign: report Federal prosecutors in New York examining Giuliani business dealings with Ukraine: report MORE has inspired the messiest political convention he has witnessed.

“This is the ugliest convention I’ve ever seen, and it’s really an extension of the candidate, of the nominee,” he said Thursday on MSNBC’s “Andrea Mitchell Reports.”

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“I mean, here’s a guy whose whole campaign started with [him saying] Mexicans are rapists and drug dealers, and [Sen.] John McCainJohn Sidney McCainThe Hill's 12:30 Report: Video depicting Trump killing media, critics draws backlash Backlash erupts at video depicting Trump killing media, critics Cindy McCain condemns video of fake Trump shooting political opponents, late husband MORE’s [R-Ariz.] not a war hero because he got captured, and 'I saw on TV Muslims, thousands of Muslims in New Jersey, cheering when [the] World Trade Center went down,' and on and on,” Franken added of Trump.

“There’s too much to chronicle. And so it’s probably not surprising that you see a convention in which there’s so much spewing of hate."

Franken noted the controversy that erupted Thursday after Trump suggested that he might not come to the aid of NATO countries if they were attacked.

“He’s their nominee and he is saying that if another NATO country is invaded he’ll decide whether or not to fulfill our obligation to NATO?” said Franken, who has endorsed Hillary ClintonHillary Diane Rodham ClintonSaagar Enjeti: Tuesday's Democratic debate already 'rigged' against Gabbard, Sanders Ilhan Omar raises .1 million in third quarter Bloomberg rethinking running for president: report MORE, the presumptive Democratic presidential nominee.

“The trust that you put in the president is that the president will do the job, will put in the work. This guy doesn’t know what he’s doing. You can’t trust him at all.”

Franken additionally mocked Sen. Ted CruzRafael (Ted) Edward CruzThe Hill's Morning Report - Lawmakers return to work as Dem candidates set to debate Cruz: 'Of course' it's not appropriate to ask China to investigate Bidens Sunday Show Preview: Trump's allies and administration defend decision on Syria MORE (R-Texas) for declining to endorse Trump on Wednesday night.

“I don’t like Ted, but I’m not alone,” he said of Trump’s former Republican presidential primary rival.

“Yes, there’s a lot of stuff that I can’t divulge,” Franken added of his Senate experiences.

“He’s not well-liked or well-respected in the institution. He’s smart. He’s a very smart guy. I’ll give him that.”

Attendees on late Wednesday jeered Cruz after he declined to endorse Trump during the Republican National Convention in Cleveland.

The awkward moment raised questions about how unified the GOP is ahead of the November elections.