WASHINGTON — Two separate functions of American journalism have emerged in the run-up to the 2020 presidential election. One is to showcase the huge field of Democratic candidates for the highest office. The other is to investigate the apparent wrongdoing of the man who currently occupies that office.

The presidential horserace is dominating cable television; CNN and MSNBC especially are shelling out hours of free air time to the Democratic contenders, 23 in number so far. One wonders how many of them are serious or just grabbing gratis exposure.

Meanwhile, the continuing inquiry into Trump is being handled largely by print news publications, especially by rich establishment newspapers like The New York Times, The Washington Post and The Wall Street Journal, as well as by independent outlets like Politico and Vox. They have focused in particular on the political and business activities of President Trump, seeking evidence of possible malfeasance that could lead to his impeachment or defeat next year.

Both topics are worthy exercises of the free press’ obligation to inform the public. But the first, the presidential nomination race, with some cable channels offering as many as five one-hour “town halls” for candidates on a single might, is turning them into low-cost show-and-tells, dominating their programming.

CNN, MSNBC, Fox News and smaller online outlets have assembled mixed casts of political surrogates and pundits and other pretenders of dubious qualification, who keep the endless chatter going day and night.

A debate has broken out over whether Democratic presidential contenders ought to appear on Fox News, as it is friendly to Donald Trump, as well as being home to his sycophant Sean Hannity.

Progressive Democratic Sen. Elizabeth Warren of Massachusetts flatly declined to appear on the network. But liberal newcomer Mayor Peter Buttigieg of South Bend, Ind., an openly gay married man, went on Fox as the best way to get his message across to all voters.

Compared to the old-fashioned networks that have spent and continue to spend millions on entertainment vehicles featuring celebrities of the worlds of show business and sports, these political talkathons now dominate the airwaves.

Thus it is left to old shoe-leather reporters of whatever news organizations may still employ them to maintain their daily vigil on the president and his chaotic and debased administration.

Many of these journalistic veterans are read in print or heard on nightly new segments as White House beat reporters, though now they are severely handicapped by Trump’s policy that has shut down the presidential press room. The role of White House press secretary has been badly damaged by Sarah Sanders’ dissembling, stonewalling and virtual disappearance from the scene, with no regular press briefing by Trump for more than two months.

Ever since he began his open war on the American press as “the enemy of the people,” Trump has concentrated on manufacturing “fake news,” undermining public confidence in our journalistic institutions as the nation’s public watchdog against malevolent rule.

If Congress has the temerity to pursue impeachment of Trump with the road map handed it by the Robert Mueller report, the Republican-controlled Senate will probably shut it down, obliging Democrats to look to the 2020 election to drive him from the Oval Office.

In the Watergate scandal that forced President Richard Nixon to resign in 1974, GOP senators were obliged by the Supreme Court release of incriminating White House tapes to tell Nixon he had to go. There is little sign yet that their party brethren of today will finally arrive at the same conclusion on Trump.

So the Democratic-controlled House committees would seem to have no choice but to subpoena testimony from Trump associates who could make the case against Trump’s unfitness to continued service between now and Election Day 2020.

In the meantime, the American news media continue to have their limited role in serving up the raw material on which a free people can base its decisions on what manner of democracy they will have.

Jules Witcover’s latest book is “The American Vice Presidency: From Irrelevance to Power,” published by Smithsonian Books. You can respond to this column at juleswitcovercomcast.net.