WASHINGTON — It took 24 years for Democrats to end the last period of Republican presidential advantage, in which issues and the makeup of the Electoral College helped Republicans win five of six elections, and to start their own behind Bill Clinton.

By 2016, the Democrats’ own stretch — winning the popular vote in five of the last six elections — will have lasted 24 years. Now, one of the biggest questions in American politics is how close Republicans are to replicating Democrats’ process of rejuvenation and winning the White House again.

The most conspicuous evidence suggests they have moved further away since Mitt Romney’s loss in 2012. In its policies and unflattering poll ratings, the Republican Party has grown largely indistinguishable from its feisty Tea Party faction. And that does not take into account demographic trends that favor Democrats.

Rank-and-file congressional Republicans forced a government shutdown last year over their leaders’ objections, and they may do so again this fall. They have buried immigration legislation of the kind that a Republican National Committee report said was vital to appealing to a growing Hispanic electorate. One promising presidential contender, Senator Marco Rubio of Florida, was pummeled by the right for even trying.