Columnist

Yes, it's a very big deal that Republicans Jeff Flake, Bob Corker, John McCain and George W. Bush are now ready to take on what Flake rightly calls President Trump's "reckless, outrageous and undignified" behavior. Their voices are the sound of the protective political wall around the White House cracking.

But the other side to this story is as disturbing as the signs of open rebellion are heartening: Both Corker and Flake have chosen not to run for reelection because they know that their views are out of line with those of the GOP's electorate.

Flake was plainly on track to lose reelection next year. The Republican congressional leadership, far from embracing Flake and Corker, moved immediately to sidestep any challenges to their "complicity" and get on with tax cuts, their sacred cause.

And House Republicans responded to the crisis in their party by announcing — a new investigation of Hillary Clinton's emails! "Saturday Night Live" writers, take note.

Trump, for once, was not deluded in suggesting in a Wednesday morning tweet that Flake speaks for a decided minority in their party: "Jeff Flake, with an 18% approval rating in Arizona, said 'a lot of my colleagues have spoken out.' Really, they just gave me a standing O!"

Flake's address on the floor of the Senate coincided with the release of an important study by the Pew Research Center that helped explain Trump's self-confidence. The report analyzed the United States' political landscape and offered an updated typology of the key partisan and ideological groups in the American electorate. The model for the typology was first created in 1987 by the late Andrew Kohut, one of his generation's wisest students of public opinion, and Pew has regularly revised it to correspond with new political circumstances.

Pew described four GOP groups: Core Conservatives, 34 percent of registered voters who call themselves Republican or lean that way; Country First Conservatives, 15 percent; Market Skeptic Republicans (22 percent); and New Era Enterprisers (18 percent). The remainder of Republicans scatter among other groups in Pew's typology.

The first two groups are particularly loyal to the GOP. Core Conservatives are who you think they are: reasonably affluent voters favoring small government and low taxes. Country First Conservatives are the folks Trumpist agitator Stephen K. Bannon loves: older social conservatives deeply skeptical of immigration and the United States' global involvement.

If Flake represents anyone, given his ideology, it would be Core Conservatives. But as of this summer, when the survey on which the study is based was undertaken, 93 percent of Core Conservatives approved of Trump's job performance and 90 percent had a favorable view of him. If this group stays with Trump, most congressional Republicans will, too. Country Firsters gave Trump an 84 percent approval rating and a 93 percent personal favorable rating.

But it's not just the most faithful Republicans who stuck with Trump. Market Skeptic Republicans, who take a dim view of "powerful interests" and believe businesses make too much profit, gave Trump a 66 percent approval rating. Among New Era Enterprisers — economic conservatives who are moderate on immigration and U.S. global engagement and relatively liberal on social issues — Trump's approval stood at 63 percent.

Trump's GOP numbers may well have deteriorated in the months since the survey was completed, and even then, there were warning signs in the answers Republicans gave to a question Pew asked about how Trump "conducts himself as president."

Among Core Conservatives, only 41 percent liked the way Trump conducts himself, 51 percent had mixed feelings and 8 percent disliked his conduct. For Country First Conservatives, the numbers are 51 percent like, 39 percent mixed and 9 percent dislike. Given how outrageous Trump's behavior is, those "dislike" figures are still very low.

His ratings were worse in the other GOP groups: Only 24 percent of Market Skeptic Republicans liked Trump's behavior while 26 percent disliked it. And in the younger New Era group, Trump was underwater: Only 23 percent liked Trump's behavior; 39 percent disliked it.

Trump's GOP opponents can still hope to demonstrate that the negative impact of how the president operates matters far more than any ideological victories he might deliver to conservatives. Trump daily proves Corker's point that it's foolish to expect he'll ever change.

But it will be an uphill struggle. Republicans such as Flake and Corker have reason to worry their party is so profoundly Trumpified that it is lost to them. At some point, they may just have to walk away.

Read more from E.J. Dionne's archive, follow him on Twitter or subscribe to his updates on Facebook.