Renegade Republicans intent on upending President Trump in 2020 are keeping their powder dry, waiting to see if legal and political controversies drive him from office first.

Political operatives and potential candidates that inhabit the loose-knit community of Republicans who oppose Trump’s re-election are eyeing June as the approximate moment for deciding on a primary challenge or independent bid. It’s a strategic delay. Some Republicans think the weight of multiple investigations could motivate the president to exit the White House after one term — especially if special counsel Robert Mueller issues a politically damaging report.

"The scenario I think we could be heading toward is Trump hitting a Mueller-induced problem where there would suddenly be several people looking at running because of the odds increasing that he won’t run again," said Rob Stutzman, a veteran GOP consultant in Sacramento, Calif., who has had discussions with like-minded Republicans about how Trump 2020 might be derailed.

[Read more: GOP operatives in key states warn Trump 2020 is slow out of the gate]

The president begins the election cycle in a position to cruise to renomination, bolstered by the overwhelming support of grassroots Republicans. But a small-but-persistent group of Republicans unhappy with his leadership remains. Some are actively attempting to recruit a credible primary challenger; others are examining the viability of an independent bid.

The Republicans most often listed as possible Trump challengers are outgoing Ohio Gov. John Kasich, who ran in 2016; Sen. Ben Sasse of Nebraska, who is up for re-election next year; Sen. Mitt Romney of Utah, the GOP presidential nominee in 2012 who was elected to his current post just last year; Maryland Gov. Larry Hogan; and former Sens. Bob Corker of Tennessee and Jeff Flake of Arizona, who sources say are unlikely to run.

Depending on the circumstances, Kasich is perhaps the most immediately prepared to mount a credible challenge to Trump, notwithstanding his prickly relationship with loyal Republicans.

But Kasich isn’t interested in waging a primary campaign that might hobble the president against the Democrats in the general election but falls short of the White House. That’s why he’s considering running as an independent. Any Kasich bid, independent or GOP, would likely rely quite a bit on New Hampshire. The governor finished second there in the 2016 primary, and his supporters in the state say he retains considerable backing for another run.

"We would not run to be a Pat Buchanan-like spoiler. That's not anything that the governor or we are interested in," said John Weaver, a senior Kasich adviser. "We have an organization in place in New Hampshire that's grown since we finished second in 2016. We have consolidated, to some degree, the anti-Trump or disparate groups around the country who are opposed to the president within the party."

Any Trump challenger who attempted to assemble a campaign in the current environment would run into major hurdles.

Republican donors who might secretly root against Trump wouldn’t openly oppose him. A GOP operative in regular contact with many wealthy contributors said they wouldn’t risk angering the president and inspiring a tweet that could damage their political or business interests. However, some might give to political nonprofit organizations that, by law, don’t have to disclose donors.

Staffing a campaign also would be difficult. Republican strategists with talent and connections wouldn’t chance losing existing clients or being blackballed by official party committees. One experienced Republican consultant connected to an individual mentioned as a possible Trump challenger said he was disinclined to join a campaign that opposed the president.

“Few Republican consultants would today get involved with a challenger. But there are a few, and I’m one of them, depending on the candidate,” said Rick Tyler, a Republican consultant in Washington, D.C., whose outspoken criticism of Trump forced him to step down from a 2018 Senate campaign.

The Trump campaign is in the process of fielding a strong national organization. The safe bet is that the president runs in 2020. But some Republican operatives who are actively exploring an intraparty challenge to Trump’s leadership believe there are various paths to mounting a credible primary campaign that would imperil his re-election, despite the logistical, financial, and political roadblocks.

Some say a successful strategy might focus on states where party rules allow independent voters to participate in the GOP primary. They're also somewhat encouraged by Republican National Committee rules that open the door for a primary challenger to win enough votes to be placed in nomination on the convention floor in Charlotte.

Nevertheless, history is not on their side. No independent or primary challenge to a president in the modern era has succeeded, though a strong showing by the late Sen. Eugene McCarthy, D-Minn., in the New Hampshire primary in 1968 helped convince President Lyndon Johnson not to seek re-election.