For months, the political world has treated Robert Mueller as the arbiter of President Donald Trump's fate: Hopeful Democrats have theorized about the damage Mueller's investigation might inflict. Suspicious Republicans, led by Trump, have cast him as leading a "witch hunt."

But this week Rudy Giuliani, the president's lawyer, offered a bracing reminder that Mueller is unlikely, in the end, to render a decisive judgment on the president.

Giuliani, citing conversations with the special counsel's team, said Mueller intended to follow Justice Department rules that make presidents immune to indictment while in office. For decades, politically appointed lawyers in the executive branch have argued that the stigma and distraction of being indicted would interfere with the president's ability to carry out his constitutional powers.

And from Watergate to the impeachment of Bill Clinton, special counsels have adhered to that standard, leaving it to Congress — and the voters — to punish presidents or forgive them for alleged wrongdoing.

Giuliani's account for now has not been confirmed by Mueller's office, and some doubt lingers over it because he has repeatedly made claims on behalf of Trump that later came into question. But if he is right, Mueller's investigation does not appear to pose a direct legal threat to Trump while he is in office.

Raising stakes for midterms

Instead, any finding of wrongdoing would be referred to Congress, putting it squarely in the realm of politics. That further raises the stakes for control of Congress this November and potentially puts impeachment or the threat of it front and center in the midterm elections. The prospect is unsettling to both parties — unnerving Democratic leaders who have strained to mute impeachment demands from the left and Republicans who worry that new disclosures about Trump could destabilize his presidency.

Rep. Jerrold Nadler of New York, the senior Democrat on the House Judiciary Committee — the body where any impeachment proceeding would initiate — said he anticipated that Mueller would either issue a report relatively early in the summer or wait until after the November elections.

"That report will or will not indicate that the president has committed serious crimes, will or will not show lots of evidence for that," Nadler said, stressing that the special counsel's findings should be made public. "I don't know that the House will have to take action, depending, but it's important that we demand transparency."

But Nadler indicated he was not among the Democrats hungering for an impeachment effort. Attempting to oust Trump without "overwhelming" evidence of wrongdoing, Nadler said, would risk "tearing the country apart."

"You don't have impeachment unless the case is so strong that you will convince a good fraction — not a majority, necessarily, but a good fraction — of the people who voted for Trump that you had to do it," Nadler said.

Sen. John Kennedy, R-La., said he expected voters would ultimately render judgment on Mueller's findings. Kennedy said he hoped Mueller would give a full report on Russian interference in American elections, and soon.

"Once he finishes the investigation, I want him to report to the American people and let the chips fall where they may," Kennedy said of the special counsel. "And I trust the American people to figure it out."

But Kennedy does not face re-election until 2022, and few politicians on the ballot this fall share his serene outlook. While some candidates on the left and right have sought to exploit the Mueller investigation in different ways, most politicians in difficult races have sought to avoid the issue.

They have largely adopted a posture of deference to Mueller, insisting the special counsel must finish his work before they judge the facts.

That day of judgment, however, may be approaching with inconvenient speed. Should Mueller unearth information implicating the president or members of his immediate family in serious crimes, it could put enormous and in many cases unwanted pressure on Congress to take action — and on congressional candidates to take a stand.

Trump and his lawyers have denied that he conspired with Russians to influence the 2016 election, or that he did anything to obstruct an investigation into Russian interference.

Thursday was the anniversary of Mueller's appointment, and Trump marked the occasion on Twitter.

"Congratulations America, we are now into the second year of the greatest Witch Hunt in American History…" Trump tweeted, "and there is still No Collusion and No Obstruction."

The president also asserted that federal investigators attempted to infiltrate his campaign.

"Wow, word seems to be coming out that the Obama FBI 'SPIED ON THE TRUMP CAMPAIGN WITH AN EMBEDDED INFORMANT,' " Trump tweeted. "Andrew McCarthy says, 'There's probably no doubt that they had at least one confidential informant in the campaign.' If so, this is bigger than Watergate!"

Impeachment efforts

Already, several dozen Democrats voted earlier this year to advance an impeachment resolution against Trump, and public opinion polls show the idea of toppling the president is hugely popular with Democratic voters. Holding back an avalanche of impeachment calls could prove difficult for the party in the event of a damning report.

Trump, meanwhile, has rallied his base by repeatedly denouncing the investigation, and strategists in his camp believe they can mobilize voters on the right by warning that a Democratic-controlled Congress would seek, in effect, to invalidate Trump's election. But that political strategy could prove difficult to sustain if Mueller furnishes extensive evidence of wrongdoing by Trump or his associates, or indicts other people close to the president.

Martin Frost, a former member of Congress from Texas who led the Democrats' campaign efforts in 1998, as Republicans sought to impeach Clinton, warned that moving against a president has the potential to backfire. In Clinton's last midterm election, Democrats gained seats when voters rejected Republican demands they punish the president's party.

"I think it's in the Democratic Party's interest to wait as long as possible before making any definitive statements on this," Frost said, adding of a hypothetical Mueller report: "If it's bad enough, then maybe it is possible for Democrats to talk about it now."

For the moment, at least, it may provide some modest relief to Republicans that they seem unlikely to have to campaign under the shadow of a presidential indictment.

Giuliani said that although Mueller was coy, a prosecutor working for him said that the special counsel's office would follow the Justice Department's policy against taking such a step. Two or three days later, Giuliani said, a lawyer in Mueller's office called another one of the president's lawyers, Jay Sekulow, and echoed that message.

"They can't indict," Giuliani said.

The department's Office of Legal Counsel, whose interpretations of the law are binding on the executive branch, has twice concluded that sitting presidents are temporarily immune from prosecution, and any criminal process against a president must wait until he has resigned, been removed through impeachment, or his term has ended.

Other scholars have disputed that claim, however. Nothing in the Constitution or federal statutes says that presidents cannot be indicted while they remain in office, and no court has ever ruled that they enjoy temporary immunity from prosecution.