In ways big and small, with implications tiny and vast, the campaign that delivered Trump the White House -- and the way he has acted since arriving in Washington eight months ago -- has totally upended conventional wisdom about what politicians say and do.

The latest example is the decision Tuesday by Tennessee Sen. Bob Corker, a Republican, to retire after two terms

In his announcement, Corker cited his commitment to being a citizen legislator as the driving force behind his decision.

"When I ran for the Senate in 2006, I told people that I couldn't imagine serving for more than two term," he said. "Understandably, as we have gained influence, that decision has become more difficult. But I have always been drawn to the citizen legislator model, and while I realize it is not for everyone, I believe with the kind of service I provide, it is the right one for me."

Which is fine! But also odd by the traditional standards of Washington.

After all, the term limits movement long ago lost any of the perceived power it had to call out members who broke their pledges to serve some sort of set time in Washington.

More importantly, Republicans are not only in the majority in the Senate through 2018 but, given the map next November, could well add a few seats to that majority heading into the next Congress. Corker still had two years -- after 2018 -- left on his term as chairman of the Senate foreign relations committee. And, if Republicans held onto their majority in 2020, he would have been the chairman of the influential banking committee and a powerful player on the budget committee as well.

In the old days, NO member of the majority party with as many prominent committee seats as Corker would have even considered retiring. It just wasn't done.

Plus, Corker was an ally of Senate Majority Leader Mitch McConnell and someone who -- until recently -- enjoyed a relatively friendly relationship with the Trump White House. Corker was considered as a vice presidential nominee in 2016 and mentioned for a slot as secretary of state in Trump's Cabinet. And, at 65, Corker is positively a spring chicken in the Senate.

Against all of those positives, Corker's explanation that he simply wanted to stay true to his roots as a citizen legislator rings hollow. Or, more accurately, it rings incomplete.

The simple fact is that life in Trump's Washington -- and Trump's Republican Party -- is just no fun for a guy like Corker. While he's a conservative, he's no ideologue. He developed a reputation as a dealmaker shortly after coming to Washington and has worked to maintain that rep in his 11 years in the chamber.

"The Tennessee Republican has been a point man on banking reform, with President Barack Obama endorsing the proposal he developed with Democratic Sen. Mark Warner of Virginia to replace Fannie Mae and Freddie Mac. His amendment to increase spending on security along the US-Mexican border helped win passage in the Senate of an immigration bill that is loathed deeply by tea party activists."

That profile has become increasingly unattractive to Republican primary voters. Corker faced the likelihood of a challenge next year form his ideological right -- spurred on by former White House chief strategist Steve Bannon. He would have started as the favorite in that race but a win was far from certain.

Then there is the more-difficult-to-quantify stress and strain of being a pragmatic and policy-focused Republican in Trump's Washington. For Corker, who thinks big policy thoughts and wants to find ways to make government work, Trump's unpredictability and yo-yoing moods -- as expressed via tweet -- had to be frustrating.

He let that frustration slip last month while talking to reporters in Tennessee. "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," said Corker . "We should hope that (Trump) aspires that he does some self-reflection, that he does what is necessary to demonstrate stability, to demonstrate competence, to demonstrate that he understands the character of our nation and works daily to bring out the best of the people in our nation."

Trump -- natch! -- attacked Corker on Twitter for those comments. "Strange statement by Bob Corker considering that he is constantly asking me whether or not he should run again in '18," tweeted Trump . "Tennessee not happy!"

The prospect of six more years of answering questions from reporters day in and day out that began "Did you see Trump's tweet ..." was surely not one that Corker relished.

Corker follows a series of other pragmatic Republicans out the door in 2018 including Reps. Ileana Ros-Lehtinen, (Florida), Charlie Dent (Pennsylvania) and Dave Reichert (Washington).

The conclusion? The "governing wing" of the Republican Party -- as Dent put it -- isn't having any fun in Washington anymore.