At the Republican National Committee’s spring meeting, the divide between those who would accept Donald J. Trump as the party nominee and those fiercely opposed to it was on display.

Despite Mr. Trump’s advantage in delegates, his opponents argue that it is not too late to stop him, an effort that relies on the complex system of rules for choosing convention representatives.Those rules have led Mr. Trump to call it “a rigged” nominating process.

Party conventions have faced those accusations before, with one of the most famous examples occurring in 1960.Former President Harry Truman resigned as a delegate to the Democratic National Convention, calling the event “a prearranged affair,” fixed to give the nomination to John F. Kennedy.

Although Mr. Kennedy arrived in Los Angeles as the front-runner, having won each of the seven primaries he entered, his selection was not a done deal.He didn’t reach the necessary vote total for the nomination until Wyoming, the final state scheduled in the roll call, pushed him over the top.

The political jockeying continued to the very end, with the convention floor briefly taken over by nondelegates who had slipped into the hall to support Adlai Stevenson, the Democrats’ nominee in 1952 and 1956.

The top Democratic Party official said the protest was “the best answer to charges of rigging for Jack Kennedy.”