Strange thing is that Stan Evans is one of the original editors of National Review. Also, Bill Buckley's second book was McCarthy and His Enemies, co-written by his brother-in-law, Brent Bozell, Jr. It was written during the original McCarthy controversy from a generally pro-McCarthy viewpoint.
The charge is false; Ann is no Bircher. So why did Buckley react to Treason that way? Because to him, the defining fight was not McCarthy against the left, but McCarthy against Eisenhower - and he still associates siding with McCarthy in that phase of the fight, with the Birchers and their absurd charge that Ike was a communist. Which was in turn a result of taking literally McCarthy's "conspiracy so vast" speech, originally directed at Marshall and Acheson.
The facts are clear enough in Evans. Eisenhower deliberately broke with McCarthy because he found his continued investigation of security cases within the Army, specifically, after Ike was already president, to be paranoid overkill, and assumed that he was fishing and making it up, based on Ike's own prior conviction that McCarthy had unjustly smeared Marshall. Ike resented attacks on "his" army and on "his" adminstration, and employed quite similar tactics to those Truman used, to try to shut McCarthy down.
Evans and Ann have pointed this out, and it is uncomfortable stuff for the establishment Republicans of that era. The leadership back then deliberately threw McCarthy to the left, seeking Strange New Respect from the media, and peace with the oldline, Wasp, new england and ivy establishment that had defended the likes of Acheson. And part of the grassroots interpretated that decision as siding with the "conspiracy" that McCarthy was hunting, and went crazy over it, as the Birchers.
They don't want anything like the Birchers brought back. They don't want to revisit the fight, either. They don't want it pointed out that they were as right as you like about Marshall and Ike personally, but it did not change the fact that they smeared McCarthy to get rid of him, and did not fight him on those more reasonable grounds - let alone just cleaning up the messes he pointed out and letting partisan chips fall where they may in the process.
Fundamentally, the want a less strident party than Ann wants. They want to get along with the press and the left better than she does. They don't want to hunt down every case in which the left destroyed people unjustifiably and force them to admit it, nor to use such past cases to teach the next generation about the modern left today. And the reason is, at bottom, that they want to govern moderately and work with these people.
Unfortunately for that sensible sounding desire, the modern left is in fact hip deep in outright treason, and refusal to call them on it has wrecked US foreign policy. Ann sees that. Evans knows it, though he is limiting himself to telling the truth about the past, rather than advocating something now.
Ann wants in particular to force NR to admit that it is the one distorting history here, that it has smeared her, specifically, and that the Strange New Respect it tries to get from the center-left by distancing itself from her and those like her, has a long and inglorious tradition of precedents, and has furthered the left's past treasons and injustices. NR reads that as an attempt to bring a kind of Birchee conspiratorial confrontationalism back into the party, which it rightly thinks would be politically deadly. But it isn't such an attempt - it is just historical truth about how the left operates, in all its gory detail, and the ones being paranoid in the matter are the folks at NR.
The right frame to read Evans is, instead, as a modern political Lord Acton, acting out his maxim that "no reputation has withstood the revelation of private correspondance". He is arraigning men who deserve it before the bar of history, where partisanship is no excuse, and moral crimes to individuals or the better cause remain. Which is the quite conservative and principled job, of upholding moral absolutism in the discipline of history.
The shallowness of the spin deployed against Evans and Ann, is right now the most conspicuous aspect of the affair. They are right, and their critics are smearing them or chasing ghosts or politically triangulating, instead of just telling the truth.