The following editorial appeared recently in the Chicago Tribune.

Between the loose cannon Donald Trump and the ultraconservative Ted Cruz, Republicans have been doing their best to give the presidential election away. But it’s worse than that: They are doing their best to drive voters into the Democratic fold for years to come.

With their targeting of Muslims, hostility to immigration reform, rejection of climate-change science and opposition to same-sex marriage, the two threaten to sharply narrow the party’s slice of the electorate.

The question is: Will the Democrats accept the favor? It’s easy to overlook how they are putting their own political future in peril. Bernie Sanders is not likely to win the nomination, but his robust challenge to Hillary Clinton makes it plain that the Democratic Party has shifted leftward just as Republicans marched the opposite way.

Sanders, remember, is a self-styled democratic socialist who always ran as an independent because he considered the Democrats insufficiently progressive. Though he is the older candidate, his support skews young. Sanders leads among men and whites, a new NBC News/Wall Street Journal poll found, but his most notable feat is beating Clinton among Democratic voters younger than 50 by a 2-to-1 ratio. This is the party base of the future.

Even if Clinton wins this time, there is a leftward riptide that she will have trouble resisting, on the campaign trail or in office.

Not that she’s trying very hard. She has said the 1994 crime bill husband President Bill Clinton signed was too harsh. She rejected a Pacific trade agreement she had previously lauded and endorsed a $15 minimum wage enacted in New York. She has tried to sound like populist firebrand Elizabeth Warren on banking issues.

Maybe she can veer back toward the middle if and when she gets the nomination. But motivating Sanders’ supporters to get to the polls will be crucial, and that need will put strong pressure on Clinton to stay in the left lane.

So it looks as though there will be a gaping hole in the middle of the political spectrum.

Looking at the two likely Republican nominees, those centrist Americans ask: “What about us?” So far, the Democratic response is: “What about you?”