Donald Trump thrives on turbulence and hard-fought battles and, as he has often said, he prizes his readiness to return every blow with one even harder than the one landed on him. This is the strategic context within which he has understood—and used—the law and the legal process. He has been the hyperactive litigant, quick to threaten and file lawsuits and convinced that he can use litigation and the law as another way to declare himself a winner. After all, he is the president who once proudly declared that he was “like a PhD in litigation.”

Now Trump seems poised to carry this same mode of operation into the defense of his presidency against what may be multiple investigations. He has hired as his lawyer for this very public challenge the same man who has supported him in his business representations—a lawyer whose professional web site notes approvingly his reputation of being the “toughest of the tough guys.”

Maybe because of the Watergate analogy, or the more recent experience with the Kenneth Starr investigation of President Clinton, we presume that a president under these circumstances would sensibly “lawyer up.” And Trump, like his predecessors, certainly has the right to defend himself. Yet in other, very material respects, this case is unlike the others. Trump’s defense—not to mention, the type of defense that Donald Trump most typically mounts—will present serious conflicts with his duties as President.

The focus of Watergate was a burglary and a cover-up; for President Clinton, it was a personal relationship that he sought to conceal through false statements under oath and other, related allegations of obstruction of a legal proceeding. In neither case could it be suggested that in answering these charges, the presidents who faced these scandals had to choose between the requirements of their defense and the fulfillment of their basic and ongoing constitutional responsibilities as Chief Executives. Of course, both Nixon and Clinton could (and did) suffer in doing their jobs from the debilitating effects of an investigation. Both also had to manage along with their regular duties concurrent congressional inquiries on the same subject, culminating in a formal impeachment process. But this adverse effect on the discharge of their presidential responsibilities was largely indirect.

So when President Clinton said as the Lewinsky matter unfolded that he intended to stay focused on the public’s business, it was a plausible claim. Well known for a capacity for “compartmentalization,” Clinton could persuade the public that he could govern in its interest while dealing with his personal legal problems: that he could keep those problems from interfering with the conduct of his official duties.

Nixon’s case is more complicated: he brought his personal defense into the heart of government, attempting unsuccessfully to misuse the intelligence services in derailing the Watergate investigation. These public misdeeds were largely ancillary to his private, self-protective purposes. Nixon never needed to block or rig the outcome of a governmental process organized to address an independently significant challenge in the country’s national security or domestic affairs—one that required urgent attention irrespective of their effects on the president’s legal affairs.

Not so in Donald Trump’s case. The investigation now underway is by no means only about President Trump and his aides—the legal implications of what they did or intended. It is a counter-intelligence examination of Russian designs and programs to interfere in the United States political process. The issues under review extend beyond intentional wrongdoing to include possible Russian efforts to enlist the unwitting assistance of Americans inside or outside the Trump political inner circle. As President, Trump bears the ultimate responsibility for assuring a full, unfettered, and brisk (albeit thorough) exploration of a possible national security threat of extraordinary dimensions. Instead, having announced that it is a “made-up story,” and having fired the F.B.I Director who was taking it seriously, he has hired a lawyer—”the toughest of the tough guys”—to help defend himself against it.

Most narrowly, the President and his legal team will prepare to defend against any allegations of obstruction arising out of his own interventions. We should not begrudge or criticize Trump for arranging for this defense. But more broadly, and with profound implications for the investigation, a lawyered-up president will now dig in against its core objective, which is to say the very one the President has derided as “made up”—the legitimacy of the investigation into Russian collusion or compromising relationships with the president’s campaign, associates, family members and others. Mr. Trump’s main points against any charge of obstruction will include the denial that there has been a legitimate investigation to obstruct. He will continue to insist that the Comey, now the Mueller, inquiry is nothing more than a fairy tale “made up” by his political enemies. He and his lawyers will want to show that he lacked the motive for a cover-up and had no nefarious purpose in demanding the FBI’s Director’s loyalty and then dismissing him, or in enlisting the intelligence community’s help in ending the investigation. His legal defense and his discrediting of the Russia line of questioning are tightly connected.

So while as President, Mr. Trump is charged with getting to the bottom of the question of Russian activity or at least not getting in the way, Donald Trump as individual has a different, conflicting interest. This interest seem certain to drive him to limit his personal exposure, by limiting or carefully shaping his official support and cooperation, in the Russia matter.

This strategic imperative will ripple throughout the investigation. His lawyers will be in touch with lawyers for other witnesses, who have their own strategic choices to make in responding to the Special Counsel’s and Congress’ requests for interviews and for subpoenas. In this sort of investigation, wagons will circle. Counsel to various individuals swept up in this matter will normally enter into formal or informal “joint defense” arrangements. They will share information for their mutual benefit, including on the question of whether they will invoke the Fifth Amendment or testify, and on the content of any testimony they give .

This is not obstruction of justice. It is more or less standard white-collar criminal defense, and we can assume that the President and his legal team will conduct it in the no-holds-barred fashion in which Mr. Trump has taken pride.

The President sees the Russia investigations as a challenge to his election and his authority. It is a danger to family members, such as his son-in-law, who is now reported to be the White House senior aide of “interest” in the inquiry. It has damaged, and continues to embroil, a close associate and friend like Flynn, for whom the Mr. Trump has exhibited great personal concern. And it could, on facts not known or established, eventually threaten his personal legal interests.

However, to do what his urgent official duties require, Mr. Trump would have to forego resorting to much of the stock and trade of the hard-nosed legal defense. He would have to largely give up the staunch, scorched-earth defense of his political and legal interests, and of those of friends and family members. This is not how he typically operates, and not what we have seen in his behavior so far.

Now the President may and surely will reply that, in pronouncing the Russia controversy to be bogus, he is delivering a judgment in the national interest that, as Commander-in-Chief, he cannot avoid making. A political motivated, contrived scandal serves only to cripple his presidency. It also interferes with major shifts in foreign policy he deems urgent, such as rebuilding a damaged relationship with Russia to allow for collaboration on matters of common interest. So, yes, he might say: he will do what he can to fight off this investigation as a metastasizing attack on his presidency.

The defect in this line of argument is that it ignores his Department of Justice’s conclusion that an independent review of the Russia matter is warranted and required, and a determination along similar lines by a Congress controlled by his own party. The executive and legislative branches are mostly united in the view that the question of Russian interference with U.S. political and governmental processes is not, in fact, bogus, even if much about this Russian activity—including its nature and seriousness—remains to be known. Moreover, the President’s insistence to the contrary is fatally infected with self-interest. It is hard to credit him with making an independent executive judgment, and whatever conclusion he has reached is not grounded in a thorough exploration of the facts that now falls to Congress and the Special Counsel to conduct.

It seems highly unlikely that the President sees or accepts this conflict of constitutional duty and private interests. But there may come a point when it cannot be denied or ignored.

Perhaps the president, in theory anyway, would have the option of temporarily stepping down under the procedures of the 25th Amendment. He would not do so because he is ill or, in a medical sense incapacitated. He would make a concededly unanticipated use of the Amendment because he has this vitally important duty that he cannot perform while pursuing his personal defense—in the terms of the Amendment, he is “unable” in these circumstances to “discharge the … duties of his office.”

But this choice on his part is unlikely in the extreme. This exceptional conflict will persist, with profound consequences for the course of this investigation and the future of his presidency.