The head of the Republican National Committee braced the party faithful Sunday for what could be the first contested nominating convention in generations, suggesting increasing odds of a showdown this summer over Donald Trump’s candidacy.

While Trump has a big lead in convention delegates, many party elders and strategists, alarmed over his ascent, are redoubling efforts to deny him the nomination. At the least, they are seeking to force a battle at the July convention in Cleveland. In multiple television interviews Sunday, Reince Priebus, chairman of the RNC, raised the prospect of a protracted convention fight with multiple rounds of voting needed to determine the winner.