Most of my writing on this site is devoted to the technical legal issues raised by Mr. Trump’s misadventures and the constitutional riddle of what constitutes an impeachable offense.  I hope readers find these discussions useful.  Nonetheless, Mr. Trump’s vulgar, tawdry, racially incendiary feud with protesting NFL players is a reminder that the path to impeachment, if it exists at all, will be opened by public sentiment, not legal argument.

Any discussion of presidential impeachment is bounded by two apparently contradictory realities. On the one hand, then-congressman Gerald Ford was right that, as a practical matter, “An impeachable offense is whatever a majority of the House of Representatives considers it to be at a given moment in history.” In the other hand, our historical practice has been to read “high Crimes and Misdemeanors” fairly narrowly and to shrink from actually removing presidents from office.

No American president has been both impeached by House and convicted and removed by the Senate. President Nixon resigned rather than face impeachment, but only after the release of the Watergate tapes caused his public support to collapse. President Clinton survived trial in the Senate not, I think, because he was factually innocent of the charges against him. Rather, his public support remained high, indeed grew, during the impeachment controversy, and a majority of the Senate concluded that his removal from office for what most people viewed as unseemly, but not disqualifying, lying about sex, would outrage the electorate.

In Mr. Trump’s case, I have identified one provable impeachable offense — the Arpaio pardon. Others have contended that what is known of Mr. Trump’s financial entanglements and of his efforts to quash the Russia investigation amount to impeachable violations of the emoluments clauses and obstruction of justice statutes.  Evidence of other conduct that could be categorized as impeachable by serious people may well emerge over the coming months. But none of it – none of it — will matter so long as Republicans hold the House and Mr. Trump holds the allegiance of 40-some percent of the electorate as a whole and three-quarters or more of Republican voters.

No majority-Republican House will ever vote to impeach Mr. Trump, or even to investigate the question seriously.  In an earlier era, there might have been enough public-spirited Republicans to open an inquiry, if the facts were egregious enough. But the extreme polarization of the House, and the death grip on the House Republican caucus enjoyed by its right-most fringes would surely foreclose such a development. Even if the Democrats flip the House in 2018 and proceed to impeachment, conviction in the Senate would require a dozen or more Republican votes.  Those votes will never be available as long as Republican senators face a credible threat of primary challenges from the Trumpian right.

Therefore, unless and until Mr. Trump loses the active support of something approaching half of the primary-voting base of the Republican party, his lease on the White House is secure until 2020. It may not be necessary that half of all Republicans openly repudiate him, but close to half must become sufficiently disillusioned that Mr. Trump’s removal would become a matter of relative indifference rather than a cause for tribal fury.  Then, and only then, will he become vulnerable to impeachment.

Which brings us back to the NFL.  There has been a good deal of brow-furrowing analysis of the perverse cleverness of Mr. Trump’s insult campaign against kneeling NFL players.  And I suppose it is clever in the sick sense that he is managing to inflame the latent hostility of fans who obsess over the game, but nonetheless privately, even subconsciously, resent the players’ wealth and status, by reminding the fans that a whole lot of these guys are black.  Trump’s genius is the sadist’s gift of finding every raw nerve, suppressed neurosis, and healing wound in the body politic and poking at it.

Mr. Trump’s sadism secures him the loyalty of the angry and the insecure who constitute a large fraction of his political base. And I’m sure that his NFL tantrum will go down well enough with many of these. But does there come a point when he has simply gone too far?  A point when the loyalty or at least amused patience of tribal Republicans begins to crumble under the weight of the ceaseless tide of insults directed at nearly every admired figure in American life?

I certainly don’t know the answer to this question.  But I can’t help but believe that getting into a fight with Lebron James, Steph Curry, the Golden State Warriors, and the whole NFL establishment is a bad move for a guy whose base is disproportionately made of folks for whom professional sports generally and football in particular are near to religion.  It would be sickly ironic if the mass affinity for Trump that survived his insults to a genuine American hero like John McCain began to crack over a cheap feud with sports stars, but somewhere there must be a straw that will break this pestilent camel’s back.