Washington (CNN) Sen. Mark Warner said his chamber's passage of the Republican tax reform bill Saturday morning was his "single worst day as a US senator," adding that the GOP's last-minute bill changes were "swamp 101."

"(A)s somebody who wanted to be a part of tax reform, and realizes we need to have a more competitive corporate rate, that realizes we need to bring back some of those American profits, there are three things about this process that just plain stunk," the Virginia Democrat said Sunday on CNN's "State of the Union."

One of the "swamp 101" provisions was a special tax break for Hillsdale College, he said.

"Friday night (when) the bill was being hand-drafted, lots of provisions were being included for special interests. One got exposed already, exempting a particular religious college in Michigan backed by the DeVos family for special tax breaks," Warner said.

Warner was referring to language that was ultimately struck from the GOP tax bill that would have given a tax exemption exclusively to the small college in Michigan, which has ties to the Trump administration, including Education Secretary Betsy Devos, whose brother, Blackwater security firm founder Erik Prince, was a graduate.

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