House Speaker Kevin McCarthy has been in a precarious position as leader ever since his marathon speakership vote in January, when the California Republican made a number of concessions to win over the 20 or so hard-right members of his party who opposed his bid. A little more than 100 days later, his authority over the GOP is still fragile—and he’s about to face his biggest test yet as House Republicans prepare this week to vote on his bill to raise the debt ceiling temporarily and slash federal spending. McCarthy and other top Republicans are hoping to get the bill on the House floor as early as Wednesday, but there is growing concern that they will be unable to muster the 218 votes needed to pass the $4.5 trillion package.