As President Trump looks at ways to get rid of the special counsel leading the investigation of Russian meddling in last year's election, the intricate rules designed to ensure the independence of such probes may be about to face their first real test.
The rules were put in place nearly 20 years ago to cope with what the Justice Department called the "extraordinary circumstances" of an investigation into possible crimes or corruption which could involve the president — the one official in whom the Constitution vests 'the executive power.'"
Given the obvious sensitivity, the regulations sought to insulate special counsels by providing that they "may be disciplined or removed only by the personal action of the attorney general" and only for specified reasons, such as misconduct or conflict of interest.
In the current inquiry by special counsel Robert S. Mueller III, Trump, who is both the chief executive and a potential target, has repeatedly signaled he wants it to end.
And if Trump is really determined and willing to take the political heat, some legal experts say, the carefully crafted rules designed to protect the independent counsel may not be enough to restrain him.
“The bottom line is that President Trump has the raw power to fire Mueller — despite it being a catastrophically bad decision that should lead to his impeachment,” said Neal Katyal, a former acting solicitor general under President Obama and the lead author of the 1999 Justice Department special counsel rules.
The Constitution puts the power of prosecution in the hands of the president, Katyal said, and that power can’t truly be limited.
The current special counsel system is a legacy of both the Watergate scandal in the 1970s and the Clinton impeachment in the late 1990s.
President Nixon decided to resign in 1974 under pressure from Republican senators rather than fight his impeachment in the House.
Afterward, a wary Congress passed a new law with high hopes of heading off another such constitutional crisis. The law authorized the attorney general to turn to a panel of judges who in turn would choose an "independent counsel" to investigate the White House in future cases.
The unintended result was to create a new Washington industry of endless, costly investigations that churned for years and often ended in no significant charges. By 1999, Republicans and Democrats agreed to let the independent counsel law die and to return the full prosecution power to the Justice Department.
That led the Clinton administration in 1999 to adopt rules under which the Justice Department agreed that in future cases, it would appoint prosecutors who were somewhat independent of that president's appointees.
But no one contends the special counsel is entirely shielded.
"The complexities of the legal issues aside," said University of Texas law professor Stephen Vladeck, "the president has a fair amount of legal authority to act, or at least attempt to act."
One option for Trump and his lawyers, Vladeck said, would be to try to end the investigation by rescinding the special counsel regulations.
Trump's lawyers could argue the current chief executive is not bound by the regulations issued in an earlier administration.
"The regulations can't trump the Constitution," said Josh Blackman, a law professor at South Texas College. "If President Clinton wanted to bind himself with those [special counsel] regulations, he could do so, but he can't bind the next president."
Such a move would likely lead to a long court battle over the legality of the special counsel rules.
Some former White House lawyers say the president is bound by the special counsel regulations as long as they remain on the books. The regulations clearly say only the attorney general can discharge the special counsel.
"That is a requirement, and it's binding on the president," said Walter Dellinger, a White House lawyer under President Clinton.
The Supreme Court appeared to endorse that view in the Nixon tapes decision of 1974. The justices cited a Justice Department regulation of that era which allowed the special prosecutor to challenge Nixon's assertion of executive privilege.
"As long as this regulation remains in force, the executive branch is bound by it," the court said in United States vs. Nixon.
On Thursday, two bills were introduced that would make it harder for Trump to ignore the current rules.
One from Sens. Thom Tillis (R-N.C.) and Chris Coons (D-Del.) would codify the current regulations into law. Another from Sens. Lindsey Graham (R-S.C.) and Cory Booker (D-New Jersey) would require any removal of the special counsel to first be reviewed by a panel of federal judges.
Trump also might deploy the "nuclear option," Vladeck said: The president simply could issue an executive order to abolish the special counsel's office and fire Mueller.
"I think the better way to put it is that Trump could assert the constitutional authority to fire Mueller and shut down the investigation," he said.
That could be risky, he added. It's not clear the Supreme Court would uphold such a move if the justices had a chance to weigh in.
But the legal theory, known as the "unitary executive" and around since the Reagan era, has gained popularity in conservative legal circles.
Under this theory, the president "is constitutionally entitled to fire anyone in the executive branch," said Peter Shane, an Ohio State University law professor.
"I think the theory is wrong, but it's out there and is part of the debate," he said.
A third option for Trump would be to work within the existing regulations and ask — or order — the attorney general to fire Mueller. That's complicated in the current case because Atty. Gen. Jeff Sessions has recused himself from any role in the investigation. Deputy Atty. Gen. Rod J. Rosenstein is the acting attorney general for any issues involving the Russia investigation, and he's already told Congress he would not fire Mueller without a clear, legal justification.
If there is a point of agreement among the constitutional experts, it is that a move to shut down the Russia probe would set off a political backlash.
Republican Sen. Lindsey Graham of South Carolina said recently that "any effort to go after Mueller could be the beginning of the end of the Trump presidency unless Mueller did something wrong." Other senators have made similar statements.
"The real question is not whether the president has a legal right to fire Special Counsel Mueller," Vladeck wrote last month, "but whether such a legal move might nevertheless provoke his current supporters in Congress to turn against him."
On Twitter: DavidGSavage
12:35 p.m.: This article was updated with details about a second special counsel bill being introduced.