Critics of the administration now worry that Mr. Kirk’s murder could be used as a pretext to move even more aggressively against those who speak out against Mr. Trump.

U.S. Deputy Secretary of State Christopher Landau on Thursday warned that Washington may take action against foreigners "praising, rationalizing, or making light" of the killing of conservative activ...

The president immediately treated the killing of his ally as a matter of top national importance, ordering flags to fly at half-mast and saying he will attend Kirk's funeral.