As Levin says, we have Bob Corker's defiance of the constitution to thank for Obama's Iran deal.
The Washington Times had a nice summary of Corker's malfeasance from Jed Babbin, here:
He sponsored a measure that required the president to submit the agreement to the Senate but turned the Constitution upside down. Under Article 2, Section 2 the president must get a two-thirds vote in favor of any treaty to make it a part of the law of the land. Instead, Mr. Corker’s provision required opponents of the deal to muster a two-thirds vote — 66 senators — to vote against it. It was a pretense to conceal another Republican cave-in to Mr. Obama. Mr. Corker’s provision passed the Senate by a vote of 98-1, Sen. Tom Cotton, Arkansas Republican, being the only negative vote. In an entirely predictable result, when the time came for a disapproval vote, Republicans couldn’t even overcome the Democrats’ filibuster to get a final vote on disapproval. After that, it was a small matter for the president to take the Iran deal to the U.N. Security Council, which eagerly approved it. What Mr. Corker had done was to enable Mr. Obama to claim Senate approval of his deal even though the Senate hadn’t done anything of the sort.
Like Jeff Flake, Corker won't be standing next year for reelection to the Senate.