Primary campaigns are often about appealing to extremes. General elections are about winning the center.

In the upcoming election both the Democrats and the Republicans will be tempted to broaden their bases by appealing to the extremes within their party. Whoever gives in to that temptation may well lose.

We are a centrist country that has always eschewed extremes. The vast majority of Americans, whether Democrat or Republican, regard themselves as moderates. That is certainly true of independents and voters who might be attracted to “no labels” type of approaches.

The so-called “progressive,” hard-left extremists within the Democratic Party are its loudest and most aggressive of its components. Yet they are the least important in terms of winning the general election. To the contrary, they are most likely to lead the Democratic Party to defeat.

The recent wave of what the press calls pro-Palestinian demonstrations — but are in reality anti-Israel and anti-American protests — are a symptom of the Democrats’ problem. These extremists have disrupted life in many parts of the country. 

They have blocked access to roads, transportation hubs, and even holiday celebrations. They have disrupted presidential speeches, classes, and other public events. They have shouted down speakers and shut down meetings. 

The demonstrators are largely comprised of three groups: radical anarchists who weaponize any issue that attacks the government; anti-Israel and pro-Hamas Muslims and Arabs; and useful idiots, especially students who are looking for issues to protest. They constitute a tiny fraction of American voters and do not represent mainstream views.

Because they are so loud, raucous, and omnipresent, some politicians and pundits mistakenly believe they will be more influential in the general election than they are actually likely to be.

It is unlikely that any of these rabble-rousers will vote for President Trump, and so the only question is whether they will remain home. If they do, it could reduce the number of Biden votes in places like New York, California, and Massachusetts, where they are most influential. Yet these states will certainly end up voting for President Biden regardless of how many far-left voters stay home.

There are a few states whose outcomes could be influenced by such voters on the left staying home. Michigan is among them, not because of the far left as such, but because it is home to a large number of Muslims and Arabs who have promised to protest the Biden administration’s support for Israel. Counteracting Michigan might well be Florida, whose large pro-Israel population could possibly make a difference by voting for Mr. Biden — unless he capitulates to the anti-Israel left.

It is also possible that the threats to stay home may turn out to be a bluff. Voters often cast their ballots for their least unfavorite candidate even if they disapprove of many of his policies, which in Michigan may be Mr. Biden. Yet even if many leftists and Muslims do decide to stay home, they are unlikely to impact the election.

What may impact the election negatively for Mr. Biden would be the perception that he is turning left to accommodate his party’s extreme liberal wing. That might well be a kiss of death. Centrists and independent voters do not want to see America fall into the hands of the far left. 

Nor do they want to see Mr. Biden abandon Israel. Mr. Trump’s advisors know this and they will campaign against any turn of Mr. Biden to the hard left or away from Israel’s right to defend its citizens, if they see the opportunity to do so.

So my advice to Mr. Biden, if he wants to be re-elected, is to ignore the “progressive” hard left and continue to stay the course as a centrist supporter of American values and American allies such as Israel.

Though I am not a Republican, I also offer my advice — as a patriotic American — to Mr. Trump. Ignore the extremists among Republicans. Become a more centrist conservative. Accept compromises about abortion, immigration, gun control, climate change, and other divisive issues. Give voters the choices they really want — between moderate conservative and moderate liberal approaches. 

Moving both parties closer to the center would be good for Americans and for our two-party system.