Senator Chris Coons is open to imposing conditions on future military aid to Israel, a sign that pressure is growing on U.S. President Joe Biden to punish the Middle Eastern ally over its deadly ground assault in Gaza.

Coons’ stance, articulated for the first time during an interview with POLITICO, could prove a headache for Biden. The senator is seen as the president’s unofficial emissary and closest ally in the Senate. Coons’ openness to conditioning arms sales to Israel could lead to more questions about why the White House isn’t pursuing that option.