Instead, Flake's opposition to Trump has consisted almost entirely of complaining, and now he's not even bothering to seek reelection to the Senate, where he could do something about whatever Trump is doing.
Flake behaves like he is helpless. That's because he is helpless. And he should think some more about why he is so helpless.
Flake is helpless because there's no real constituency in America for what he favors: low taxes and spending, openness to immigration and trade, international collaboration where America honors its commitments, and polite public behavior.
There is one coalition of voters that favors a much larger and more active government than Flake wants. Many of these voters share a portion of Flake's values (they may share his commitment to openness and politeness, for example) but they also oppose him on various social issues where he is conservative and they are liberal. Flake does not have a home in the Democratic Party with these voters.
The other coalition of voters is the one Flake relied on all along to get elected. But it turns out they don't care very much about some of the policy ideas Flake thought were important. And they outright oppose him on others, like immigration. And many of these voters have come to view nastiness and crudity as virtues, since they think politeness norms have been weaponized by an establishment that wants to exclude them — or just because they are jerks.
It was essentially an accident that Flake and elected officials like him were able to harness the Republican electoral coalition for so long to back an agenda that excluded policies those voters cared about (like immigration restriction) and included ones they opposed (like cutting Medicare). Now that's over, and he has nowhere to go.
A look at the non-helpless anti-Trump senators gives a clue about why Flake can't seem to do anything about the things he cares about.
Republican Sens. Lisa Murkowski and Susan Collins have broken extensively with Trump to much greater effect than Flake. Their defections have worked because their formulation of personal decency plus policy moderation is saleable to a large slice of the electorate. ...
Collins and Murkowski are able to be a lot more soft-spoken than Flake; their anti-Trump actions have done most of the talking. They've had a lot of effect on policy in Trump's America. And they don't seem to intend to leave the Senate anytime soon.
--Josh Barro, Business Insider, on power through bases of leverage