It is a genuine worry for many Democrats. As the number of candidates running for the 2020 Democratic Party nomination for president goes steadily upward, the fear grows that a non-mainstream candidate from the party fringes will get the nomination and be a weak candidate in the November general election.

Presidential primaries and caucuses, such as the early caucuses in Iowa and the early primary in New Hampshire, are plurality elections. A large field of candidates can run in a plurality primary or caucus, split the vote, and the winner can score a victory with a low percentage of the total vote and little real support from a majority of those voting. At last count, more than a dozen candidates have talked about running in the 2020 Democratic Party presidential primaries and caucuses.

There is a cure for this problem, and the cure is established and operating well in Colorado. The cure is, in each political party, to hold a nationwide runoff primary in all 50 states and D.C., one runoff for the Democrats and the other for the Republicans. This will produce political party nominees for president, one Democratic and the other Republican, who will have shown at the national ballot box they have broad voter support in their political party.

Such National Presidential Primary Runoff Elections would have to be created by law by the U.S. Congress and signed by the president. That way all 50 states would be required to participate in the nationwide runoff in both political parties. There would be no Electoral College as there is in the general election in November. The votes from all 50 states and D.C. would be added together and a majority vote would determine the Democratic nominee in one runoff primary and the Republican nominee in the other.

Congress will have to act now to institute this badly needed reform. Obviously, waiting until the caucuses, primaries, and state conventions begin in January of 2020 will be too late.

So it would go like this. The presidential caucuses, primaries, and state conventions would be held in all 50 states, just as they are currently, from about January to June of 2020. As done currently, state laws would govern when the caucuses/primaries/state conventions are held and what rules would apply. But in July, after all 50 states had held caucuses or primaries or state conventions, the top two candidates in each party with the highest number of delegate votes would enter each party’s July nationwide runoff. The winner of the Democratic Party runoff and the winner of the Republican Party runoff would face each other in the general election in November.

One strength of this proposal is it would leave the current complex calendar of presidential primaries, caucuses, and state conventions unchanged. Iowa, New Hampshire, and other states would not have to give up their preferred positions in the existing system. The change would be instituted only after the familiar run of primaries, etc., had gone its full length course to the middle of June.

The problem of too many candidates running for major party presidential nominations is not going to go away. There is a reason so many people are running for president these days. Lately comparative outsiders have been gaining nominations and the presidency. Barack Obama in 2008 and Donald Trump in 2016 are examples of lesser known candidates who have gained a major party nomination and won the White House. “If anyone can win,” so the logic goes, “why shouldn’t I be a candidate? Electoral lightning just might strike me.” As a result, relatively unknown politicians, such as former Colorado Gov. John Hickenlooper and former San Antonio Mayor Julian Castro, are taking the presidential candidate plunge.

About 25 percent of Coloradans are familiar with this runoff election concept. Denver and Colorado Springs use it in their elections for mayor. Pueblo is currently installing such an electoral system for electing its mayor.

In Denver and Colorado Springs, if one candidate gets more than 50 percent of the vote for mayor in the first round, no runoff is required and the candidate with majority support is declared elected. The same would apply at the presidential level. If, after holding primaries and caucuses in all 50 states, one candidate had 50 percent or more of the delegate votes, that candidate would be declared the party nominee for president and no runoff would be held.

Tom Cronin and Bob Loevy are retired political science professors who were longtime members of the faculty at Colorado College in Colorado Springs.