Former White House counsel John Dean famously told Richard Nixon that there was a “cancer on the presidency.” That cancer ultimately claimed not only Dean (who pleaded guilty to a felony) but 69 government officials who were charged (with 48 found guilty) on Watergate-related crimes. Most notably, it led to Nixon’s resignation in disgrace.

It all began as a small bungled burglary at the Watergate that led to the discovery of slush funds, dirty-trick political operations and cover-ups. It is a cautionary tale for any White House: The real danger of a scandal is not the discovery of the primary cancer but the risk of metastasis, or spreading of a cancer to all parts of a body.

The key in medicine and the law is to act before a cancer spreads to unknown parts. This could be the objective behind a reported offer of the Trump legal team of a “deal” with special counsel Robert Mueller. With new allegations mounting against the president, the team is reportedly seeking a closure of the investigation in return for an interview. The question is whether this offer is too late and too limited to deal with the threat.Metastasis occurs when cancer cells break away from a primary cancer and travel through the blood or lymph system in other parts of the body to form new cancers. The irony in Trump’s case is that the original investigation began with an allegation that he or his campaign colluded with the Russians to interfere with the 2016 elections. I have previously expressed my skepticism that a criminal case against Trump could be made on such collusion on the currently available evidence.

However, the mandate given to Mueller is a virtual pathway for metastasis. Deputy Attorney General Rod Rosenstein mandated that Mueller may investigate “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump.” In addition, Mueller is allowed to investigate “any other matters within the scope of 28 C.F.R. § 600.4(a) — including perjury, obstruction of justice, destruction of evidence and intimidation of witnesses.” Finally, he is allowed to investigate “any matters that arose or may arise directly from the investigation.” That is a mandate that can easily take the investigation to any part of the Trump business, legal and political dealings.

If Trump were to agree to such a sit-down, it would have been smarter to do so many months ago before new allegations emerged. That is how you confine a cancer — with early and overwhelming action. With every month, however, the potential list of topics for an interview (and the evidence gathered) expanded exponentially, from secured loans to strippers to the Seychelles. On the available evidence, a properly prepared Trump could do an interview of collusion and even obstruction without causing greater harm. It is certainly a risk given the president’s penchant of ill-advised statements. Trump can navigate the obvious risk of false statements in a narrow, well-defined interview, but the scope of the risk is now far broader than it was.

The Stormy Daniels payoff by Trump’s longtime lawyer, Michael Cohen, in an example of the risk of waiting. A narrow scope now depends largely on Mueller’s sense of restraint or propriety. Unlike the unrelated charges against former campaign chairman Paul Manafort, these allegations are directly related to the election and would easily constitute a matter that arose in the course of his investigation. Indeed, the best hope for the White House is that the notoriously buttoned down, patrician Mueller might be repelled by the thought of delving into alleged romps with porn stars and Playboy bunnies.

The Trump team can legitimately demand a list of areas for such an interview in advance under a decision of the D.C. circuit court involving former Agricultural Secretary Michael Espy, who was accused of 30 corruption counts involving gifts and travel under the Clinton administration. Former President Clinton advanced excessive claims of privilege to try to protect himself and his aides from answering questions. He failed spectacularly.

First, the Supreme Court ruled that he had to agree to a deposition in a civil lawsuit by one of the women accusing him of sexual assault. Second, the courts reaffirmed, for both Clinton and Espy, that the limited privilege against answering questions can be overcome with a showing of a legitimate evidentiary need. This is particularly easy to show in a criminal investigation. Moreover, the White House would be hard pressed to argue that dealings on prior business deals or payoffs to porn stars involve core presidential decisionmaking.

However, the courts have applied a balancing test in defining the scope and necessity of questions. That means Mueller must show that he cannot get this information from other sources and that he has well-defined, reasonable areas of inquiries. That can reduce the surprise element but not necessarily the risk. If Mueller were to put Daniels or financial dealings on that list, the interview is less likely to be a cure as opposed to a catalyst for legal risk.

Trump could maintain that he will agree to an interview solely on the original collusion allegations. Mueller then will have to decide whether he wants to pull Trump into court in a subpoena fight over the other topics. The optics could appeal to the White House in reaffirming that the investigation is now far afield from the original mandate and that the president has cooperated in addressing the original allegations of knowledge of Russian hacking or election interference.

That strategy would treat the original cancer over a year after it showed up on X-ray. Even if Mueller agrees to an initial interview on collusion or a narrow category of questioning, it does not mean he cannot demand answers on the remaining areas. Clinton testified at least seven times on different allegations during his presidency.

Whatever deal is struck or rejected, the next step is likely to be the most critical for both Mueller and the White House. In refusing to answer questions categorically, the White House could trigger a court fight that works, ultimately, to the advantage of Mueller. The White House would likely get a list of topics (and limitation of time and topics), but Mueller would likely win on the right to force an interview.

With privilege arguments negated, Trump would be left three choices: invoking his Fifth Amendment privilege (with obvious political risks), refusing to comply (risking an order of contempt), or answering a range of difficult questions (with the risk of false allegations or incriminating statements). There was a time when a limited interview might have sufficed. However, Mueller has metastasized. It now depends on how aggressive he will be, but both the treatment options and the outcomes are becoming more limited.

Jonathan Turley is the Shapiro Professor of Public Interest Law at George Washington University. You can follow him on Twitter @JonathanTurley.