So Michael Flynn is gone from a job that he should never have had in the first place. The question now is whether his departure marks the final gasp of a political scandal or just the beginning of a crisis that could conceivably oust Donald Trump from power.

As we now know, in late January, Acting Attorney General Sally Yates warned the White House counsel that Flynn’s phone calls with Russian officials were of such a nature that he had opened himself up to blackmail. Yates and the Justice Department’s investigators had discovered, from intercepts of those phone calls, that Flynn had discussed U.S. sanctions policy—essentially telling them not to react to President Obama’s economic penalties against Russia, or to his expulsion of 35 Russian diplomats in the wake of Vladimir Putin’s manipulation of the election, because Trump would reverse the measures after he took office.

This we know. But what if Trump knew the subject of Flynn’s conversations at the time? What if he had authorized Flynn to discuss sanctions relief or had been otherwise complicit in the arrangement? Then Trump himself would be vulnerable to Russian blackmail. This has been the underlying concern in the various probes of Trump’s possible financial ties to Russia. It was the essence of the “dossier” assembled by the British ex-spy Christopher Steele, detailing the kompromat—the term in Russian intelligence circles for compromising material—that the Kremlin allegedly had on Trump.

The probes of Trump’s financial ties have not panned out. Steele’s dossier is as yet unverified, though U.S. law-enforcement agents are finding it increasingly plausible, as many of the meetings it recounts—the names, dates, and places—match the real records. Flynn’s fate—the revelation that he had discussed sanctions policy with Russian officials, that he lied about it to Vice President Mike Pence and others, and that Trump did nothing about this for weeks after the acting attorney general warned him to beware—greatly boosts the odds that more investigations will take place, whether by the FBI, various counterintelligence agencies, Congress, or all of the above.

If there’s more to be discovered, it is now more likely than before that it will be discovered. If Flynn’s scandal sticks to Trump, or if it turns out that Flynn was acting at Trump’s instigation all along, and if Trump’s motives seem to resemble what the dossier suggests, then Trump is in trouble. Congressional Republicans and their base have managed to overlook, reinterpret, or dismiss Trump’s many lies, evasions, and acts of carelessness in the brief span of his presidency so far. But one thing that they might not be able to ignore, the thing that might go a bridge too far for all but the most diehard of his supporters, would be clear evidence that the president of the United States is secretly beholden to a foreign power.

Whether or not this scenario comes to pass, Trump’s White House, chaotic from the outset, is currently in turmoil. In Flynn’s wake, the president’s foreign policy apparatus, which has been spinning in several directions, is rudderless, and his already severe isolation is intensified.

Flynn was the ultimate loyalist, a retired three-star general who abandoned the officers’ apolitical creed to join the Trump campaign in full lather, to the point of retweeting the craziest anti-Clinton conspiracy screeds and screaming at the Republican National Convention, “Lock her up! Damn right!” Through the election, the transition, and the first few weeks of Trump’s presidency, Flynn was a constant presence, one of the few fully trusted insiders, the only confidant whose sole portfolio was national security, and Trump seemed to rely on him for more than that. According to the Huffington Post, Trump once phoned Flynn, of all people, at 3 a.m. to ask whether a strong dollar was good or bad for the economy. (Flynn didn’t know, and why should he?)

Tensions were already emerging between Flynn and Trump’s secretary of defense, retired four-star Gen. James Mattis. Many in the foreign policy community, and in Congress, had put huge hopes on Mattis as a counterweight to Flynn’s influence. The hopes have so far borne fruit as Mattis convinced Trump to back away from a draft executive order—which Mattis learned about from a newspaper report—that would have reopened CIA black sites for detainees and reconsidered the ban on torture. Flynn was the main force behind the order; Mattis was on record as firmly opposing the idea.

What happens now? Retired Lt. Gen. Joseph Keith Kellogg, the National Security Council’s chief of staff, has taken over as acting national security adviser. Kellogg is a veteran of the Vietnam and Gulf wars with experience at staff jobs in the Pentagon and the White House. And he was listed as a foreign policy adviser to Trump during the campaign, though they aren’t seen as having a close relationship.

Kellogg is reportedly one of the names on a shortlist of replacements for Flynn. But the most intriguing, even provocative name is Gen. David Petraeus, who is said to be meeting with Trump this week. Petraeus, of course, comes with baggage. In 2013, he resigned as CIA director after it was revealed he was having an extramarital affair with his biographer, Paula Broadwell. The following year, he was charged with sharing classified material with her and for making false statements to the FBI. (He pleaded guilty to reduced misdemeanor charges, was fined $100,000, and is still on probation.) The national security adviser does not have to undergo Senate confirmation, but given concerns about the mishandling of classified information by Flynn, Hillary Clinton, and Trump himself after his high-profile briefing about North Korea’s missile test in the middle of the Mar-a-Lago dining room, this may weigh against his chances.

Then again, Petraeus is widely admired in the foreign policy community, whose denizens are increasingly disturbed by Trump’s judgment and competence. Petraeus may be a route to relief. He has actually participated, alongside Cabinet secretaries, as a member of the NSC Principals Committee. He has global experience in national security policy and has a strategic mindset.

But this experience may end up a debit. Petraeus is a consummate operator, and, despite his discrediting in some circles, he still has connections throughout the national-security bureaucracy. When President Obama was considering Petraeus as possible chairman of the Joint Chiefs of Staff, White House aides advised against it, seeing him as too independent, too politically savvy, and too invested in his own agenda. Trump’s advisers may have the same concerns. Especially in this administration, where the president and his inner circle know little about foreign policy, and where so many senior positions are still unfilled in the State and Defense Departments, Petraeus could run the show—manipulating Trump far more than the other way around. Finally, Petraeus was on good terms with Hillary Clinton, even sitting in on a campaign advisory council. Though he never endorsed her, this could be the crucial blow against him in Trump’s eyes.

In that sense, a possible compromise candidate—and another name on the list—is Vice Adm. Robert Harward, a former Navy SEAL who has served as director of defense issues on the NSC staff, as the Joint Chiefs’ representative at the National Counterterrorism Center, and as deputy commanding general of U.S. Central Command. This last post may be most significant of all as the commanding general at the time was Mattis, and the two got along well. If Trump relies on Mattis’ recommendation, Flynn’s replacement may well be Harward.

But who knows? Newspapers have printed supposed shortlists for various top slots in the Trump administration, and sometimes they’ve turned out to be false. Remember when the secretary of state was going to be Rudy Giuliani, Mitt Romney, or John Bolton?

So how about this as a wild card for Flynn’s replacement? Robert Gates—former secretary of defense, CIA director, and deputy national security adviser: respected in all corners.

Trump asked Gates for advice on nominating a secretary of state—and he took it, naming Rex Tillerson, whom he’d never met before. Gates probably doesn’t want the job. He loathes much about Washington: His tell-all memoir, Duty, was so brutal about so many people, it amounted to a plea and a warning to future presidents not to give him a job in the capital again. And yet a close acquaintance of Gates’ told me in a phone conversation Tuesday that he could see Gates taking the job if Trump offered it. “Being asked to serve the country by presidents is his Kryptonite,” the acquaintance said. “It’s the one thing he is helpless against.”

Whoever replaces Flynn, his biggest challenge won’t merely be to stabilize the USS Trump in stormy waters but to keep the whole ship from capsizing.

This article has been updated with new information since it was originally published.