On Tuesday morning, the White House received some welcome news: Steve Bannon, the president’s chief-strategist-turned-arch-frenemy, was refusing to answer questions posed by the House Intelligence Committee regarding the Trump campaign’s ties to Russia, claiming a bizarre form of executive privilege and uniting the committee, which has been plagued by partisan infighting, in collective irritation. But the reprieve was short lived: lawmakers answered Bannon’s silence with a subpoena, and though they concluded his hearing after more than 10 hours, they reportedly expect him to reappear before the committee “soon.” At his subsequent hearing, Texas Congressman Mike Conaway told Politico, “We’re going to get answers from Mr. Bannon.”

As if to underscore the lingering danger for Donald Trump, news also broke Tuesday that Bannon had been subpoenaed by special counsel Robert Mueller, in an apparent effort to prevent the White House from blocking his testimony. And, according to a source close to Bannon, the former adviser is more than ready to talk. “Mueller will hear everything Bannon has to say,” the source told the Daily Beast. His cooperation is doubtless a source of concern for the president, who counted Bannon among his closest allies during the campaign.

Though Bannon didn’t join the Trump campaign until its final months, he worked in the West Wing during a number of critical events. Most notably, Bannon’s tenure overlapped with James Comey’s firing—the focus of Mueller’s obstruction of justice investigation—and he was around when Trump allegedly dictated a misleading statement on Air Force One about Donald Trump Jr.’s June 2016 Trump Tower meeting with a Russian lawyer. Mueller is also expected to question Bannon about remarks he allegedly made to author Michael Wolff concerning the Don Jr. meeting and Jared Kushner.

The flurry of activity isn’t limited to Bannon, either. Former campaign manager Corey Lewandowski and Hope Hicks, the White House communications director and one of Trump’s longest-serving aides, are also scheduled to appear before the panel this week. Hicks, unlike Lewandowski, will almost certainly claim executive privilege protects her from testifying about events that took place after the inauguration. But thanks to Bannon, lawmakers now have a guidebook for circumventing such a claim.

And while Mueller is nearing the end of his witness list, his probe is not likely to wind down any time soon. Despite the assurances of Trump’s lawyers, the investigation is expected to stretch into next year, with the criminal trial of former campaign chairman Paul Manafort and his deputy Rick Gates likely to begin in September at the earliest. Republicans, who were already bracing for electoral slaughter in 2018, worry the intrigue could overshadow the midterms, putting the entire party in a bad light. “The timing of the Manafort-Gates trial will dictate major coverage going into early voting,” veteran G.O.P. strategist John Weaver, told Politico. “And this is without knowing for certain how many more indictments and how much closer this Siberian political cancer gets near the Oval Office.”

Also looming large before the White House is the nightmare possibility that Trump will be called to testify. Mueller has reportedly indicated to the president’s legal team that he is interested in interviewing Trump, but it’s not clear if and when such an interview would take place, or what shape it would take. Any presidential testimony would be assured to distract the American public and further hamstring the G.O.P. in its effort to hold onto majorities in the House and Senate. And while the notoriously litigious Trump has certainly sat through his fair share of depositions, the stakes in this case would be much higher. Trump is famously evasive and misleading under questioning—prone to exaggeration and tangents that could amplify his legal exposure at the hands of what some Trump loyalists fearfully call Mueller’s “killers.” As Washington defense lawyer Justin Dillon told the Associated Press, “They’re not going to let the B-team question Donald Trump.”