The Democratic Congressional Campaign Committee has come under fire for interfering in a handful of Democratic primary races around the country. In trying to clear the primary field for the more moderate Democrat candidate they think will be the strongest in the general election, party leaders have drawn the anger of some in the party who think that the mere attempt to do so is corrupt and undemocratic.

I beg to differ.

No other political party in democracies in the world has abdicated its leadership role as much as America’s political parties have, weakening themselves and their ability to govern in the process. Partisan leaders have essentially given away the most important power political parties have — to determine who can run and win under the party’s banner. This power now rests exclusively with those who vote in the primaries.

This is not to say that there is no role for primaries. But the pendulum between the party’s leaders choosing its candidates and primary voters choosing its candidates has swung so far in the direction of the primary voters that even the smallest, most modest efforts to intervene in nomination races are deemed illegitimate.

The D.C.C.C. controversy erupted this week when the House Democratic whip, Steny Hoyer, was secretly taped by Levi Tillemann, a candidate in Colorado’s Sixth Congressional District primary. Asked by Mr. Tillemann if Mr. Hoyer would like him to clear the way for Jason Crow, an Army veteran who many people think is the stronger candidate, Mr. Hoyer agreed.

This episode followed one earlier this year in which the D.C.C.C. released some research on Laura Moser, a primary candidate in Texas’ Seventh Congressional District. It was a ham-handed attempt to push her out of the race, and the attention may have helped her secure a spot in a runoff.

Mr. Tillemann’s move, in releasing the tape to the press, seems to have backfired. Melissa Byrne, a former Bernie Sanders staffer and leader in the progressive movement, tweeted her agreement with Mr. Hoyer — calling Mr. Tillemann “an entitled guy expecting to get support because of family legacy.”

But Ms. Byrne, like others on the Democratic left, is unhappy with much of the D.C.C.C.’s interference. Democratic leaders have intervened in, by my count, 14 primary races, suggesting, usually gently, that someone run for another seat or clear the field for the stronger candidate. Is this legitimate?

My answer is an unqualified yes. That’s what party leadership is all about.

Democratic leaders remember all too well the failure of Republican leaders in 2010 to take control of the Senate. In the 2010 midterm elections it was the Republican Party that was riding high, fueled by the energy of the Tea Party movement and hostility to President Barack Obama’s health care plan. They won the House of Representatives, but while they picked up six seats in the Senate, they came up short of control.

Had Republican leaders been able to intervene effectively in the primary races, they may very well have taken the Senate, if not in 2010, then in 2012. To cite one example, in Delaware, had they been able to nominate former Gov. Mike Castle instead of the activist Christine O’Donnell, they might have taken the seat vacated by Vice President Joe Biden. Ms. O’Donnell may be the only Senate candidate ever who said, “I’m not a witch,” and who didn’t know what was in the First Amendment.

Are party leaders always right? Of course not. But they are different from the activists who often dominate the party primaries because they are more concerned with electability than with ideological purity. Party leaders have the job of winning nationally; Democrats are painfully aware that not all congressional districts are Berkeley, Calif. In 2018, roughly 55 congressional districts are potential swing districts, according to the Cook Political Report.

A quick look at those districts shows why. Of the 14 the D.C.C.C. has intervened in, only five have a positive Democratic Partisan Voter Index — a measure invented by the political analyst Charlie Cook to show the historical tendency of a congressional district to vote one way or the other — and the P.V.I.’s are minuscule, ranging from +1 Democratic to +3 Democratic. One district is evenly tied. The other eight districts have Republican voting histories that range from +1 to +13 and averaging about +6 Republican. In those districts, the right candidate can make all the difference.

Left-wing Democrats frequently argue about the need to mobilize the base as a reason to run progressive candidates. But the strongest part of the Democratic base consists of African-Americans, and among the districts the D.C.C.C. has intervened in, only two have African-American populations that are in the double digits, and the average African-American population in these swing districts is only about 7 percent. The Hispanic population in many of these swing districts is larger, ranging from 1 percent to 42 percent, and Democrats may be counting on them to vote Democratic in response to President Trump’s immigration policies.

In those districts, the name of the game will be to turn out Democrats but also to move some white voters into the Democratic column. If ever there was a year for Democrats to pull this off, 2018 is it — as the special elections of moderates in Virginia, Alabama and Pennsylvania have shown. Progressive Democrats could find themselves celebrating in November if they let the party leaders do their job.

Elaine Kamarck is a senior fellow at The Brookings Institution and the author of “Primary Politics: Everything You Need to Know About How America Nominates Its Presidential Candidates.”

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