It's really hard to describe the political/ideological direction of this criticism/criticism of criticism.
Kristol is a piece of shit neocon.
But he's to the left of Trump based on being more libertarian and less reactionary.
He's being criticized by someone that purports to be a traditional conservative.
Traditional conservatives are now being reconsidered to be left of neoconservatives in contemporary analysis given that they've wholly adopted the rightmost domestic policy and favor farther right foreign policy.
However, the criticism is distinctly coming from the right on the basis of him not mindlessly toeing the party line and the critic calling him an epithet associated with the left.
The party line in the case of this criticism contains approving of action that would be broadly considered left of the conservative and neoconservative position: using diplomacy over military action with former Cold War enemies.
But the motivation for the position is distinctly of a right-wing purpose and principle: being hostile to foreign enemies
A person (Frum) that is certainly to the left of both men is lamenting the rightward shift of the party to the point that Kristol is considered unacceptably left on an issue in which he's taking the rightmost position.
I guess it just hinges on the right-wing principle that not having principle and internal conformity to hierarchy is the greater value than the principle of foreign aggression.