https://www.corker.senate.gov/public/index.cfm/iran-nuclear-agreement-review-act

“After more than a year of bipartisan work and a veto threat from the White House, I am pleased to see this bill become law so that any final nuclear agreement with Iran will have to go through Congress where the American people will have a say and lawmakers will have a vote,” said Corker. “I appreciate the strong bipartisan support for this effort that demonstrates Congress’s determination to prevent Iran from getting a nuclear weapon. With the role of Congress now guaranteed, the administration must address the many significant concerns raised by Congress, and our negotiators should take advantage of the added leverage to force further concessions from the Iranians so that any agreement reached is verifiable, enforceable and can assure the American people Iran will not be able to develop a nuclear weapon.”

https://www.washingtonpost.com/blogs/post-live/wp/2017/07/26/transcript-securing-tomorrow-with-david-ignatius-and-sen-bob-corker/?utm_term=.eadf721b89b7

The Iranian agreement requires that the President certifies their compliance every 120 days. The ONLY reason that Trump hasn't decertified is because that Corker keeps saying "they are in compliance:

So you look at where we are, there’s some nuance to this certification. What it actually says is that they are implementing the deal. Iran is implementing the deal. They do have technical violations that take place. Most of them have not been what I would—it’s like a loan covenant. This is the way I’ve talked to the president, “Mr. President, we’re in loan covenant.” There’s a technical issue and then there are material breaches that matter, right? Well, right now, they’ve had some technical non-compliance but they get back into compliance from time-to-time.

http://www.cnn.com/2017/08/17/politics/bob-corker-criticizes-trump-charlottesville/index.html

"The President has not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful," Corker said, according to a video posted by local news website Nooga.com.
"He has not demonstrated that he understands what has made this nation great and what it is today, and he's got to demonstrate the characteristics of a president who understands that," Corker added.

https://www.nbcnews.com/meet-the-press/video/full-corker-won-t-support-gop-tax-plan-if-it-adds-to-deficit-1059037763567


In an exclusive interview on Meet the Press, Sen. Bob Corker (R-Tenn.) tells Chuck Todd that if the GOP’s new tax reform plan adds a penny to the deficit he won’t support it.