The Republican-controlled Senate could force a stalemate on judicial nominations, leaving dozens of seats vacant, or compel the Obama administration to propose judges who might appeal to conservatives. And this is all without a U.S. Supreme Court opening in sight.

Judicial nominations were a centerpiece of partisan fights on Capitol Hill since President Barack Obama’s second term began in 2012, with Republicans accusing the administration of packing one prominent court — the U.S. Court of Appeals for the D.C. Circuit — with judges who would back the White House agenda. Federal appeals courts have served as the battlegrounds over the Affordable Care Act, environmental regulations, voting rights and abortion laws.