Washington (CNN) Roger Stone is known for hyperbole, but his latest graphic warning should worry Donald Trump.

The political trickster said Tuesday, a day he pleaded not guilty to seven charges laid by special counsel Robert Mueller , that Trump's presidency is in mortal peril because the Russia investigation amounts to a "speeding bullet heading for his head."

Stone's comment, to "Breitbart News Daily" on Sirius XM radio , added to soaring anticipation, fueled by a remark by acting Attorney General Matt Whitaker on Monday, that the probe could soon end with Mueller's final report.

And it raised the question of whether Trump's repeated claim of "no collusion" fired off in scores of tweets and comments to the press, is a sufficiently broad defense to the existential threat that Stone perceives from Mueller's work.

The indictment of Stone, Trump's longest serving political adviser, refocused attention on whether Trump and his team crossed legal and ethical lines during an effort to defeat Hillary Clinton in an election that featured a simultaneous Russian meddling operation.

The key question for Mueller has always been whether there was a criminal conspiracy by members of Trump's team to cooperate with Moscow's bid to make him President.

So far, he has offered no proof of such a bombshell finding, in a forest of indictments, court filings, one trial and convictions of people around the President in a probe that appears to be getting ever closer to the Oval Office.

If Mueller does establish such behavior, it would answer the puzzling question: Why have so many people around Trump -- at great costs to themselves -- repeatedly lied about ties to Russians?

Or, it's conceivable -- if the special counsel could conclude that though there was evidence of a cover-up -- it was not motivated by a desire to hide a crime, but was meant to spare Trump the political embarrassment of noncriminal links to Russia?

But even if that is the case, Mueller's voluminous filings and other publicly available information have established a pattern of behavior by Trump and aides that tore at norms of behavior during campaign season and shows clear disrespect for the integrity of a presidential election -- part of the fabric of US democracy.

It is likely to fall to the Democratic-led House to consider whether such activity is unethical and in such conflict with American values, that it merits further action -- potentially even impeachment.

A record of questionable electioneering

There is already no doubt the Trump team was ready to go to extreme lengths in 2016 to win.

In one of many staggering revelations about Russia in 2017, The New York Times reported that Trump's son, Donald Trump Jr., wrote in an email "I love it" when told a senior Russian official had "dirt" to hand over on Clinton in a subsequent meeting in Trump Tower in New York.

A more recent bombshell raised more doubts about the Trump camp's observance of electoral propriety. The President's former lawyer Michael Cohen admitted paying adult film actress Stormy Daniels a $130,000 hush payment in violation of campaign finance laws at the direction of the President.

Then, when Cohen pleaded guilty to a charge lodged by Mueller in November, he said he had lied about the duration of a project to build a Trump Tower in Moscow. He originally said discussions ended in January 2016 but corrected that to say they continued as late as June 2016.

That left open the possibility that Trump had not only lied when he told Americans he had no business ties to Russia, but that he saw his campaign -- a form of public trust when he should have been promoting America's interests -- as a way to grease the wheels to a deal worth hundreds of millions of dollars.

Another question that Mueller could clear up is why Trump's former campaign chairman Paul Manafort offered proprietary polling data to Konstantin Kilimnik , a longtime business associate with ties to Russia intelligence.

The episode emerged from a botched campaign filing this month by Manafort's lawyers. It is not known whether the uber lobbyist was acting alone, possibly in an effort to funnel information to Ukrainian oligarchs to whom he was in debt.

There was immediate speculation that Manafort was acting at the behest of other campaign operatives and the polling data might have helped the targeting of social media disinformation campaigns in key swing states by Russian intelligence. Mueller alleged in a separate indictment that a Kremlin-linked troll farm spent millions to influence Americans on social media, though the charges did not describe any coordination with Trump's team.

Trump often showed disdain for accepted standards of behavior in campaigns. For instance, the then-Republican nominee called on Russia to find 30,000 missing emails from the private server Hillary Clinton used while secretary of state.

In August 2016, Trump was personally warned by senior US intelligence officials that foreign adversaries including Russia would likely attempt to infiltrate his team or gather intelligence about his campaign.

In October, US intelligence agencies went public with findings that Russia had directed efforts by DCLeaks and WikiLeaks to release Democratic emails stolen by its spies.

Yet the candidate Trump repeatedly praised WikiLeaks for the emails that badly damaged the Clinton campaign from the stump.

The public warning from the intelligence agencies coincided with the release of an "Access Hollywood" tape that contained shocking audio of Trump making lewd comments about women.

Less than an hour later, Wikileaks dumped a new batch of emails that appeared to have been designed to take the sting out of an October surprise that threatened to derail Trump's entire campaign.

Jerome Corsi, a conservative author and conspiracy theorist, told CNN in November that Stone had called him several times that day to ask him to get in touch with WikiLeaks founder Julian Assange to get him to release more material. Stone denies this.

Stone pleaded not guilty in court Tuesday to seven criminal charges of false statements, witness tampering and obstruction.

He was not charged with conspiracy, though the indictment described how Stone allegedly coordinated with Trump campaign officials about his outreach to WikiLeaks.

In one intriguing passage, Mueller alleged that "after the July 22, 2016 release of stolen (Democratic National Committee) emails by (WikiLeaks), a senior Trump campaign official was directed to contact STONE about any additional releases and what other damaging information (WikiLeaks) had regarding the Clinton Campaign."

The sentence sparked speculation about whether the person giving that direction, was Trump, or a member of his family. Even if it was Trump, it would not necessarily be a sign of a crime -- but could put him in jeopardy if he solicited information from WikiLeaks he knew was illegally obtained.

Stone is a flashing warning sign

Even without clarity on whether the President directed Stone's activity, his presence close to Trump during the 2016 campaign is casting a suspicious light on the strategy the President pursued to win.

Stone is a link between the Watergate storm, when he worked for President Richard Nixon's notorious dirty tricks gang, and the Russia intrigue -- potentially the biggest Washington scandal since the one that felled the 37th President.

"Stone will do anything to win," Princeton University history professor Julian Zelizer recently said on CNN. "I think a lot of Republicans shudder to see him back in the news right now, literally flashing the Nixon signs and people are making that comparison between President Trump and President Nixon."

If Mueller does not establish the activity during 2016 adds up to a criminal conspiracy, Congress will have to decide whether it needs to act in defense of the US electoral system. If it does, it wouldn't be the first time, and lawmakers may look to history for guidance.

In an appendix to the final report of the Senate Select Committee on the Watergate scandal , which he chaired, North Carolina Sen. Sam Ervin defined that drama as an effort "to destroy, insofar as the Presidential election of 1972 was concerned, the integrity of the process by which the President of the United States is nominated and elected."

Should Congress decide Trump is guilty of a similar transgression, with or without a recommendation by Mueller, it must then work out whether it meets the standard of a high crime and misdemeanor, the standard for impeachment.

A debate is likely at that point over whether wrongdoing before a President is elected requires the ultimate sanction against a commander in chief.

After all, Nixon was already in office when the President's men set out to stain the integrity of the 1972 election.

Corey Brettschneider, author of the recent book "The Oath and the Office: a Guide to the Constitution for Future Presidents" says that a candidate who undermines elections cannot be taken seriously when they later take an oath to defend the constitutional system.

"Certainly, cheating in an election or committing illegal acts to influence an election not only undermines a future president's integrity, it represents an existential threat to democracy, especially when it comes to colluding with a foreign government," Brettschneider said.

"If Trump cheated on the way to becoming president, he betrayed his oath to defend the basic law that underlies our system of self government," he said.