WASHINGTON -- In a party that overwhelmingly supports President Donald Trump, a few naysayers are popping up, raising the prospect that Trump could face more opposition from within his own party as he seeks re-election to a second term in 2020.

However, unseating Trump will be no easy feat. The president has the power of incumbency, with nearly 8 in 10 Republicans approving of Trump’s overall job performance in a recent poll, and Trump has brought in $57 million in the second quarter of this year alone, excluding money donated to the Republican National Committee.

But, there are a few Republicans who don't seem to be passengers on the Trump train.

Trump is already facing one official challenger in the GOP primary. Former Massachusetts Gov. Bill Weld announced his White House bid in April. Weld ran as Gary Johnson’s running mate on the Libertarian Party ticket in 2016.

Joe Walsh, a one-term tea party-backed GOP congressman from Illinois turned conservative radio host, said Thursday during an interview on CNN that he is considering a 2020 primary challenge to Trump.

“I’m strongly, strongly considering it. That’s — again, I’m not trying to be cute or coy,” Walsh said. “I’ve told you before — if somebody’s going to get in there and go after him … it’s got to be done soon.”

In a New York Times op-ed last week, Walsh wrote, “I didn’t vote for Mr. Trump in 2016 because I liked him. I voted for him because he wasn’t Hillary Clinton.”

William Kristol, a prominent conservative and “Never Trump” Republican, is encouraging Walsh to run. Kristol is the former editor of the now-defunct conservative magazine The Weekly Standard.

Walsh has been publicly critical of Trump, including the president's fiscal decision-making and racial rhetoric. Walsh also called the 2018 Russia–United States summit in Helsinki “un-American” after Trump publicly seemed to side with Vladimir Putin over the U.S. intelligence community regarding Russia's interference in the 2016 election.

"In Mr. Trump, I see the worst and ugliest iteration of views I expressed for the better part of a decade. To be sure, I’ve had my share of controversy." Walsh wrote in the op-ed. "On more than one occasion, I questioned Mr. Obama’s truthfulness about his religion. At times, I expressed hate for my political opponents. We now see where this can lead. There’s no place in our politics for personal attacks like that, and I regret making them.

"The fact is, Mr. Trump is a racial arsonist who encourages bigotry and xenophobia to rouse his base and advance his electoral prospects," he also wrote.

Additionally, George Conway, a vocal Trump critic and husband of Trump aide Kellyanne Conway, tweeted his support for a possible Walsh run.

Walsh’s public talk about a possible White House run comes after former Rep. Mark Sanford, R-S.C., appeared on Meet the Press on Sunday and said he is considering a primary challenge to Trump.

“There’s been a drumbeat over the last year of people who I admire, who are not crazy, who are very thoughtful saying we need to have this conversation,” Sanford, who is also a former governor of South Carolina, said.

More:Former South Carolina governor says Trump doesn't deserve re-election, is considering GOP primary challenge

Both Walsh and Sanford have said they intend to make a decision about challenging Trump by Labor Day.

Additionally, the Washington Post reports that Jeff Flake, a former Arizona senator and another "never-Trumper," said he has taken numerous recruitment calls in recent days from GOP donors rattled by looming signs of economic turbulence and who are eager for an alternative to Trump.

Flake has also said that it is better for a Democrat to win in 2020 that Trump, declaring, "Four years is difficult enough to unravel some of the damage" caused by the Trump administration, Flake said in March.

"Yes ... and this notion, this narrative that's been built up, that Donald Trump is the only one that can cobble together the Electoral College and win is just a fallacy," Flake also said in March.

More:Cindy McCain says there is no 'voice of reason' in GOP, nearly a year after John McCain's death

And the prospect for a fifth GOP primary challenger to Trump has cropped up. Former Ohio governor John Kasich will head to New Hampshire next month to “take a look at things” after experiencing “an increase” in overtures this summer, an adviser said. The Washington Post first reported Kasich's upcoming trip.

Speculation about the prospect of one or more new GOP primary challengers to Trump comes after weeks of very public criticism of the president by Anthony Scaramucci, the short-lived White House communications director who recently withdrew his support for Trump. Instead, Scaramucci has declared Trump “unstable” and unfit for office.

He revealed he is in the process of forming a super PAC to run advertisements against his former boss.

More:Scaramucci says he will start and fund a super PAC to 'dismantle' Trump

Scaramucci called his past support for Trump a mistake and is seeking to take action in the political arena against the president. He also ridiculed against Trump on Twitter, comparing the president to the Game of Throne's Night King and calling Trump a "bully."

The view that Trump is a bully who must be removed from the political scene by someone on the conservative side of the political spectrum is one shared by Walsh ho wrote as much in his New York Times op-ed.

“We need someone who could stand up, look the president in the eye and say: 'Enough, sir,'" Walsh penned. "'We’ve had enough of your indecency. We’ve had enough of your lies, your bullying, your cruelty, enough of your insults, your daily drama, your incitement, enough of the danger you place this country in every single day. We don’t want any of this anymore, and the country certainly can’t stand four more years of it.'”