WASHINGTON — Conservative political activist Charles Koch suggested Sunday that Democrat Hillary Clinton would be a better president than the Republican contenders, although he stopped short of saying he would support the former secretary of state if she ends up with the nomination.

The billionaire, who along with his brother, David, has been a prolific donor to Republican candidates and groups, criticized the tone of the GOP presidential primary campaign. He cited it as the reason the brothers have not contributed to any campaigns, including efforts to derail Republican front-runner Donald Trump.

In the interview on ABC’s ‘‘This Week,’’ Charles Koch also said Bill Clinton had done a better job than George W. Bush in controlling government growth while president.

‘‘So is it possible another Clinton could be better than another Republican?’’ correspondent Jonathan Karl asked.

‘‘It’s possible,’’ Koch responded, adding, however, that her rhetoric concerns him.

Koch said he has not and probably will not back any Republican in the waning weeks of the primary campaign.

He slammed Trump’s call for a ban on Muslims entering the country as ‘‘antithetical to our approach, but what was worse was this ‘We’ll have them all register.’ That’s reminiscent of Nazi Germany. I mean that’s monstrous.’’

Koch was referring to comments Trump made, then backed away from, in the fall suggesting he was open to use of a database to track Muslims.