CAMBRIDGE, Md. — Perhaps no issue is more vexing for House Republicans than their looming, unavoidable responsibility to raise the debt ceiling.

Immigration reform is politically explosive, but optional. If the House Republicans’ renewed effort to overhaul U.S. immigration law runs into trouble, they can simply set the issue aside. However, as the majority party in the lower chamber, they must approve an increase in the federal borrowing limit by the end of February or risk defaulting on U.S. debt.