THERE CAN now be no doubt: The Russia meddling story is not just smoke but fire. Donald Trump Jr.’s interactions with Russians during last year’s presidential campaign were abnormal and alarming. An incriminating email chain has made it impossible for the administration to deploy its always flimsy argument of last resort — that the whole story is just “fake news.”

Not only Mr. Trump but also presidential son-in-law Jared Kushner and then-campaign chairman Paul J. Manafort are involved. Following a string of misleading and false statements, Americans must also wonder: Were other Trump associates involved? Did other meetings take place? Was President Trump aware of them? What more did the Trump camp know about Kremlin support for the Trump campaign?

And then there is this recurring question: How long can the rest of the Republican Party prioritize partisanship and agenda over decency and patriotism?

The emails were released by the younger Mr. Trump after he learned that the New York Times was about to publish them. They show that in June 2016 a publicist who had been involved with Donald Trump’s 2013 Miss Universe pageant in Moscow offered the president’s son “official documents and information that would incriminate Hillary [Clinton].” This “very high level and sensitive information” would be from “the Crown prosecutor of Russia,” an apparent reference to Russia’s prosecutor general. It would be passed on as “part of Russia and its government’s support for Mr. Trump.”

Donald Trump Jr.’s reply was damning: “If it’s what you say I love it.” In subsequent emails, it was explicit that he would meet with a “Russian government attorney” in order to get the information.

The younger Mr. Trump and his apologists claim that he responded as would any campaign operative seeking dirt on an opponent. No. A ny ethical operative confronted by a foreign power’s attempt to meddle in this way in U.S. elections would refer the matter promptly to the Federal Bureau of Investigation.

Instead, Mr. Trump was enthused, drawing Mr. Manafort and Mr. Kushner into a meeting with someone he believed to be a Russian government attorney. Even if the Trump camp got no dirt on Ms. Clinton out of that meeting, the Russians could have used the email chain and subsequent meeting as leverage over Mr. Trump and Mr. Kushner, who is now a top White House adviser. Mr. Trump’s enthusiasm may also have communicated to the Kremlin that the Trump camp would welcome Kremlin election meddling. The Russians went on to run an anti-Clinton hacking campaign.

What now? The president’s sole comment on the matter, relayed Tuesday by principal deputy press secretary Sarah Huckabee Sanders, is that “my son is a high-quality person and I applaud his transparency.” On Monday, Ms. Sanders herself said that “the only thing I see inappropriate about the meeting was the people that leaked the information about the meeting after it was voluntarily disclosed.” That’s the only inappropriate thing? A responsible president should have something to say about the gross inappropriateness of this meeting and, speaking of transparency, about how and when he learned of it.

Senators questioning Christopher A. Wray, the president’s nominee to lead the FBI, in a Wednesday hearing must demand that he detail any conversation he had with Trump administration officials and commit to cooperating fully with special counsel Robert S. Mueller III in his investigation of the Trump-Russia connections. Lawmakers must pass a tough sanctions bill holding Russia accountable for its election meddling.

And Republican leaders, including Senate Majority Leader Mitch McConnell (Ky.) and House Speaker Paul D. Ryan (Wis.), must finally decide: Is this really okay? Are they really prepared to debase themselves in defense of a president whose closest advisers may have welcomed underhanded interference in America’s election from a hostile foreign power?