If you tell someone you’re a dentist, a patient will eventually show you his or her gumline.

When you tell people you’re a political consultant, they tell you what they think of elected officials.

This is what I’ve been hearing from New Yorkers about Mayor Bill de Blasio: “Oh, he’s awful. Who’s out there to beat him?”

The answer on the Democratic Party side, it turns out, is no one. De Blasio impressively recaptured his party’s nomination in Tuesday’s five-candidate primary with 75 percent of the vote. If many city Democrats think he is awful, Tuesday didn’t show it.

Except, possibly, in turnout, which was emphatically subpar for the mayor. Only 15 percent of registered Democrats turned out Tuesday, the third-lowest percentage in NYC history. That could mean three things: 1) Lots of Democrats are disappointed with de Blasio’s performance. 2) Primary voters considered the race a formality. 3) The line for Hillary Clinton’s new tome was even longer than reported.

Republican mayoral candidate Nicole Malliotakis hopes option “1” is the true one. The Staten Island-Brooklyn assemblywoman needs lots of Democratic votes to be competitive on Nov. 7 — plus lots of “blanks” (unaffiliated voters).

To say running as a Republican is an uphill fight might be the understatement of the week. Democrats have a 6-to-1 registration advantage over Republicans in NYC.

But lightning does strike in New York when an incumbent is perceived by some as aloof, incompetent or lazy. Fortunately for Malliotakis, de Blasio checks all three boxes with many voters.

The ongoing MTA subway mess won’t help him, nor will his terse relationship with the NYPD. The mayor’s propensity to sleep through the alarm clock is an easily lampooned character nugget that Malliotakis is already exploiting on TV.

Malliotakis also will have to contend with two minor candidates, Bo Dietl and Sal Albanese, running on third-party lines. But neither should draw many votes.

Based on registration, it is impossible for a Republican to win the New York City mayoralty — and yet candidates running on the Republican line, Rudy Giuliani and Mike Bloomberg, have held City Hall in 20 of the last 24 years.

Could it happen again? With de Blasio’s help, anything is possible.

William F. B. O’Reilly is a consultant to Republicans.