FOR THE past week, former Trump campaign chairman Paul Manafort and his business associate Rick Gates have been under house arrest following their indictment by special counsel Robert S. Mueller III. A campaign staffer with contacts linked to the Kremlin is now cooperating with Mr. Mueller's probe into election interference. The Justice Department may bring charges against Russian officials responsible for the hacking of the Democratic National Committee. Despite President Trump's best efforts, it's increasingly apparent that the White House is not going to be able to brush off the mounting evidence of Kremlin meddling.

The charges against Mr. Manafort and Mr. Gates don't concern election interference — though normally a campaign chairman's having laundered $75 million, much of it from pro-Kremlin political actors, would be scandal enough. Far more damning is the account of campaign foreign policy adviser George Papadopoulos, who appears to have been providing Mr. Mueller's team with information for months. After meeting a Kremlin-linked professor, Mr. Papadopoulos learned that the Russians had "dirt" on Democratic presidential candidate Hillary Clinton. He repeatedly sought to connect with Russian officials and to broker a meeting between Mr. Trump and Russian President Vladimir Putin. And he was encouraged by at least one campaign official, Sam Clovis, who now serves as a senior White House adviser to the Agriculture Department.

In April 2016, the professor hinted at a trove of Clinton emails. In June, Donald Trump Jr. took a meeting with a Russian lawyer in the expectation of receiving "dirt" on Ms. Clinton — and, according to the lawyer, may have offered up policy concessions in exchange. Mr. Papadopoulos never succeeded in arranging the gathering between the two leaders, and the younger Mr. Trump labeled his meeting a dud. But in July, WikiLeaks began releasing emails hacked from the Democratic National Committee — which the senior Mr. Trump cited with glee.

By The Post's count, nine of Mr. Trump's associates had direct contact with Russian officials during the campaign and presidential transition. This includes former foreign policy adviser Carter Page, who coordinated a trip to Moscow in July 2016 with campaign officials. It also includes Attorney General Jeff Sessions, who reportedly rejected Mr. Papadopoulos's pitch for a Trump-Putin meeting but is facing renewed scrutiny of his congressional testimony regarding his knowledge of campaign contacts with Russian officials. In the room along with Mr. Sessions when Mr. Papadopoulos made his pitch was then-candidate Trump, who now says that he doesn't "remember much about" the meeting.

It is beyond dispute that the Russian government sought to help the Trump campaign and that some campaign officials were open to overtures from Russia. The question is how far that cooperation went and who on the campaign was aware of it. Did Mr. Papadopoulos mention the Kremlin's trove of Ms. Clinton's emails during the meeting with Mr. Trump and Mr. Sessions, for example? The president's tweeted declarations of "NO COLLUSION!" are not sufficient.