Nothing too exciting on today’s tax-reform-oriented spate of Sunday programming except for Trump’s new public enemy number one, Bob Corker, getting a national platform to renew his feud with the president. He’s the lead guest on “Face the Nation,” where he’ll discuss his doubts about Trump’s leadership, the political demise of Jeff Flake as the party turns populist, and, er … a 2020 primary challenge?

Sen. Bob Corker of Tennessee did not rule out a run in 2020 against President Donald Trump when asked about it by reporters Friday, saying he’s focused on the next 14 months of his term and isn’t thinking that far ahead…

“You know, I don’t know what I’m doing next Sunday,” the senator responded when reporters asked about a potential presidential bid.

Corker said it was far too soon to say if he would want a strong Republican primary challenge of Trump, whether by him or someone else.

His approval rating in Tennessee has gone from 52/27 in February, before he and Trump started exchanging rhetorical gunfire, to 45/41 now. Trump’s been hurt too, though: His own approval in the state now stands at 50/40, down from 51/32 eight months ago.

Speaking of 2020, another guest this morning, Chris Christie, had this to say about Trump on Friday:

New Jersey Governor Chris Christie said he’d back Donald Trump again if he runs for a second term, but he isn’t sure the president would want another four years in the White House.

“If he runs again I would support him, yes, but I’m not so sure what would happen,” Christie said during an interview Friday on NBC’s “Today” show. “Four years is a long time, and especially for someone who has not spent a lifetime in politics, so I think those years affect him differently, so I’m sure the president will make whatever decision is best for him and his family and the country.”

He’ll be asked to elaborate on that on “Face the Nation” and “State of the Union,” both of which are having him on to look back on his two terms as governor as his time in office winds down. How does it feel to go from party star to serious presidential contender to Trump lackey to unemployed in the span of about six years? We’ll find out.

Elsewhere, John Kasich will be on “Fox News Sunday” to say Kasich-y things about Trump and the state of the GOP. The full line-up is at the AP.