There are crucial moments in history when leaders must put aside petty rivalries and partisan politics and work together to address existential threats or other looming dangers.

Now is such a time.

Republican leaders in Congress need to stand with Democrats to proclaim publicly and unequivocally that President Trump is wrong — wrong when he doubts Russia’s interference in U.S. elections, wrong when he distances us from our allies in the European Union and elsewhere, and wrong when he separates children from their parents.

Trump is wrong on so many fronts, and his errors are imperiling America’s standing in the world and its democracy at home. His bizarre behavior at the Helsinki news conference with Russian President Vladimir Putin on Monday, when he failed to affirm what even his own intelligence chiefs have acknowledged about Russian interference in U.S. elections, was just the most recent example.

Yet the silence of Republicans, for the most part, has been deafening. And shameful. And cynical.

California’s congressional Republicans need to stand up, starting with the powerful House Majority Leader Kevin McCarthy. We know he’s not blind to Trump’s failings — he was caught on tape in 2016 joking privately: “There’s two people I think Putin pays: [Rep. Dana] Rohrabacher and Trump.” But publicly he has been unwilling to speak out, and he has remained one of the president’s closest allies in Congress.

Speaking of Rep. Rohrabacher (R-Huntington Beach), he continued to defend Russia and Trump this week, saying, “We meddle all over the world at a much higher rate than what Moscow does.”

Rep. Tom McClintock (R-Elk Grove) defended Trump as well. “I don’t think insulting Putin at a joint press conference would have contributed to better relations with Russia,” McClintock said in a statement to the San Francisco Chronicle.

Rep. Devin Nunes (R-Tulare) hasn’t made a peep this week that might be construed as a criticism of Trump, although as House Intelligence Committee chairman he ought to know better.

Others who haven’t taken a stand: Reps. Jeff Denham (R-Turlock), Rep. Paul Cook (R-Yucca Valley) and Doug LaMalfa (R-Richvale).

A few brave Republicans, including Rep. David Valadao (R-Hanford), had the courage this week to make it clear that they believe Russia meddled in the election. But most did not call out Trump by name in their statements, and most are facing tough reelection battles against Democrats.

The Russia dispute is not about politics or ideology, but about real foreign interference in the basic mechanisms of democracy, and Trump’s denial of the evidence.

No more apologetics. No more equivocation. No more sitting on the sidelines. It is time — well past time, really — for Republicans to summon up the courage to tell the president when he is wrong. If they fail to do so, voters should hold them accountable in November.