WASHINGTON — The vow by Senate Republicans to block whomever President Obama nominates to fill the sudden vacancy on the Supreme Court presages a prolonged election year struggle, but the clash is less a new front against the White House than an escalation of a battle that had begun at the appeals court level before Justice Antonin Scalia died.

Since Republicans took control of the Senate in January 2015, the process that would enable Mr. Obama to fill vacancies on the 12 regional federal courts of appeal has essentially been halted. Mr. Obama has managed only one appointment because Republican senators have refused to sign off ahead of time on nominees for judgeships in their states — a traditional step before a president makes a nomination.

In the weeks before Justice Scalia’s death, influential conservative groups and commentators called on Senate Republicans to ensure that Mr. Obama appointed no more appeals court judges.

Among those commentators was Ed Whelan, a former clerk to Justice Scalia and a prominent blogger. He said in an interview Monday that conservatives could not compromise over any appointments to the upper ranks of the judiciary — including the appeals courts, which get the last word on matters the Supreme Court does not review and often serve as a breeding ground for future justices.