A growing number of Republicans on Capitol Hill have raised concerns about President Trump’s expanding war against drug cartels carried out without consultation or authorization by Congress, and are pressing for more information and involvement in a campaign whose legal basis remains murky. Most in the group have not expressed explicit opposition to the strikes that have been carried out so far against boats in the Caribbean Sea and, this week, expanded to the Pacific. The vast majority of Republicans have enthusiastically rallied behind them, and this month, all but two of them voted to block a measure that would...