Julián Castro is the latest Democrat to drop out of the 2020 presidential race. He will probably receive more press coverage today and tomorrow than he has on any other day since he announced his candidacy. But unlike other Democrats who have thrown in the towel, Mr. Castro should continue to have a significant impact on the presidential campaign.

As the race’s only Latino, extremely well versed in policy and comfortable on the stump and the debate stage, Mr. Castro is in a unique position:

If and when he endorses one of his former rivals, he will be a huge asset to the fortunate candidate.

This is not because Mr. Castro, a former San Antonio mayor best known nationally for being a housing secretary in the Obama administration, has a large base of voters to throw anyone’s way — if he did, he wouldn’t have been dropped from the last two Democratic debates. Nor is it because he has a big roster of donors to pass on to the candidate who wins his backing.

It’s because Mr. Castro was the deftest communicator among all the 2020 contenders and probably one of the deftest communicators in presidential politics over the last few decades. In particular, he was skilled at making policy arguments with a smile while simultaneously doing the unpleasant but very necessary rhetorical wounding of those he tangled with. Mr. Castro’s performances this year recalled the ruthlessness, back in the Republican primary debates of 2007, of Rudolph Giuliani’s “sanctuary mansion” charge against Mitt Romney, the effect of which was crushing for Mr. Romney.