The president clearly believes if he gives an inch on the what-Russia-did part — if he concedes that Russia made an effort to disrupt the election — his adversaries, who want to discredit his election, undermine him, and force him from office, will take a mile on the get-Trump part. That’s consistent with how Trump approaches other problems; he doesn’t admit anything, because he knows his adversaries will never be satisfied and just demand more.
But Trump’s approach doesn’t work for the Trump-Russia probe. There’s no reason he could not accept the verdicts of the House Intelligence Committee, the Senate Intelligence Committee, the Intelligence Community, and, yes, Mueller, that Russia tried to interfere in the election. There would be no political loss, and, in fact, great political gain, for Trump to endorse that finding.
At the same time, there is nothing wrong with Trump fighting back hard against the get-Trump part of the investigation. Voters know that Democrats, Resistance, and NeverTrump activists have accused Trump of collusion for two years and never proven their case. Mueller has charged lots of people with crimes, but none has involved collusion. That could still change — no one should claim to know what is coming next from Mueller — but Trump, as a matter of his own defense, is justified in repeating the “no collusion” and “witch hunt” mantras.