President Trump said Wednesday that Herman Cain is a "wonderful man," but it will be up to him to decide whether to go forward with a nomination to the Federal Reserve's seven-member board. (Molly Riley/AP)

PRESIDENT TRUMP’S plan to put a pair of unqualified partisans on the Federal Reserve Board can succeed only with the cooperation of the Senate, which is controlled by his fellow Republicans. Accordingly, it presents the GOP majority and its leader, Sen. Mitch McConnell (Ky.), with yet another test of their willingness to stand up for the integrity of key American institutions, even if it means clashing with the president — and the voter “base” over which he holds so much sway.

Thus far, the results of this political gut check appear — mixed. On the encouraging side, no Republican senator has yet publicly endorsed potential nominee Herman Cain, a Trump acolyte, except for Mr. Cain’s fellow Georgian, Sen. David Perdue. Mr. Cain, a former pizza chain chief executive and regional Fed official, is best known for his run for the GOP presidential nomination in 2012 and, unfortunately, the sexual harassment accusations that ended it. Between those charges and his slender credentials as a monetary policy expert, it’s small wonder that even senators from a Trump-dominated party would hesitate to embrace a Cain nomination. “I feel that we can’t turn the Federal Reserve into a more partisan entity” by installing Mr. Cain, Sen. Mitt Romney (R-Utah) has said. “I think that would be the wrong course.”

Other Republican senators have settled for making their concerns known privately to White House officials.

This is what passes for speaking truth to power in today’s GOP. It beats the alternative, though, which would be to let Mr. Trump have his way without even passive resistance. And that brings us to the discouraging side of the ledger, which is the rather warmer reception Senate Republicans are giving the president’s other Fed candidate, Stephen Moore. Mr. Moore, a tax-cut promoter on the op-ed pages who has opposed monetary easing when a Democrat, Barack Obama, was president — but favored it more recently under Mr. Trump — has been aptly described by President George W. Bush’s top economic adviser, Greg Mankiw, as “a perfectly amiable guy [who] does not have the intellectual gravitas for this important job.”

Nevertheless, certain senators who should know better are acting as if Mr. Moore’s lack of credentials is itself a credential. “Steve’s nomination has thrown the card-carrying members of the Beltway establishment into a tizzy,” Sen. Ben Sasse (R-Neb.) has said, “and that says little about Steve and his belief in American ingenuity, but a lot about central planners’ devotion to groupthink.”

You can already see an ostensible compromise shaping up: The Senate will get Mr. Trump to back off from nominating Mr. Cain (whose confirmation hearing could turn into yet another embarrassing #MeToo moment for the Republicans) in return for signing off on Mr. Moore. This would not be good enough. The Fed’s job is too important, and its integrity — actual and perceived — too precious a national asset to risk setting a precedent in favor of mediocrity and political influence. Republican senators who properly understand their institution’s advise-and-consent role must understand that the right answer to both of these proposed nominations is the same, and it is “no.”