Manchester, New Hampshire (CNN) Republican Sen. Jeff Flake, a vocal critic of President Donald Trump, delivered a series of verbal blows against the President while making a stop in the early primary state of New Hampshire as he continues to mull a possible GOP challenge in 2020.

"I hope that someone does run the Republican primary, somebody to challenge the President," he said Friday after a man in the audience asked if he'd make a White House run. "I think the odds that I will are long, but I've not ruled it out."

Flake's message targeted the "Never Trump" movement, as he sought to paint himself as a conservative alternative to the President.

"I stand before you today, the rarest of species, the American conservative. Americanus, Never Trumpus. Subgenus: RINO," he quipped. "There's a scurrilous rumor afoot that we're not only rare but endangered. I don't believe it."

The senator from Arizona, who was facing a tough re-election bid and decided not to run for a second term , spoke at the Politics & Eggs series, a must-do stop for potential presidential contenders hosted by the New England Council and the New Hampshire Institute of Politics at Saint Anselm College.

In the year leading up to the 2016 New Hampshire primary, 18 candidates or potential candidates spoke at the event, including Trump, who would go on to win the state's GOP primary by a landslide. Trump is set to return here Monday for an event focused on the opioid epidemic.

At the event, candidates traditionally sign wooden eggs handed out to the audience. On Friday, the eggs were already emblazoned with "Presidential Primary NH 2020."

Flake argued that Trump's rhetoric and style will eventually wear on the electorate and a return for civility will be in demand.

"People I think are increasingly repulsed when the President belittles or ridicules those on the other side, refers to them as losers or clowns or makes fun of their intelligence," he told reporters after his speech. "That's not a politics that plays well in New Hampshire. I hope it never does."

Trump, however, dominated in New Hampshire in the 2016 Republican primary, defeating a slate of other Republican candidates who were also preaching a message of civility.

But Flake is counting on the pendulum swinging away from Trump's brand in 2020. He pointed to the special election in Pennsylvania this week in which a Democrat is poised to win a US House seat in a Republican district that Trump won by nearly 20 percentage points in 2016, as well as other recent elections that have signaled a Democratic wave in the upcoming midterm elections.

"We are not appealing to a broader electorate. You can drill down hard on the base, you can have a great rally and have a lot of people excited, but that doesn't translate into electoral success these days," he said. "You can only drill down so hard on the base."

In his speech, which resembled remarks he gave at the National Press Club on Thursday in Washington, Flake described Trump as a "chaotic" President who has "no strategic brilliance" and has damaged the country's institutions. "It's well past time for us to put country before party. We've tried the other way for too long. We've done our worst, now it's time to do our best."

Flake's anti-Trump crusade this past year has marked a stunning rebuke of a president from a senator of the same party, and while some Republicans have criticized the President, none have matched the degree to which Flake has scorched Trump. His biggest complaints involve the President's attacks on the media, his track record of telling falsehoods and what Flake describes as "dysfunctional" leadership from the White House.

Trump has returned the fire. He told a small group of Republicans he was prepared to spend $10 million on defeating Flake in the primary, and he publicly offered support on Twitter for one of the senator's GOP challengers last year when it appeared Flake would run for re-election. He's also referred to the senator and former US congressman as "Flake(y)" and "unelectable" on Twitter.

While the Democratic bench is filling up with, by some estimates, close to two dozen potential candidates, the list of possible Republican challengers is much shorter, with Flake, Ohio Republican Gov. John Kasich, Sen. Ben Sasse of Nebraska and Sen. Ted Cruz of Texas most frequently mentioned, among others, by pundits.

Of the group, Flake has been the most directly outspoken against the President. He delivered a major speech on the Senate floor targeting Trump and wrote an entire book blasting his own party for enabling Trump's success.

"Never has a party abandoned, fled its principles and deeply held beliefs so quickly as my party did in the face of the nativist juggernaut," he said Thursday at the National Press Club. "We have become strangers to ourselves. Even as we pretend everything is fine."

The last major primary challenge against a sitting president was in 1992, when former Nixon adviser Pat Buchanan unsuccessfully ran against George H.W. Bush. Any candidate who challenges Trump faces long odds. According to a poll by the University of New Hampshire, 60% of Republican primary voters say they plan to vote for Trump in the 2020 GOP primary, as of last month.

Fergus Cullen, a former New Hampshire state GOP chairman, noted that many incumbent presidents who have drawn serious primary challenges have failed to win re-election in the end: President Lyndon Johnson in 1968, President Jimmy Carter in 1980 and Bush in 1992.

"One question is whether the purpose of the (2020) challenge will be to win or to serve as a vehicle for principled members of the party to signal disgust," said Cullen, who identifies as a "proud" Never Trumper.

Flake acknowledged that a primary bid will be a difficult fight due to the President's heavy support among the base.

"Right now I can say this is the President's party, Republican primary voters in Arizona and elsewhere are firmly with the president by large majorities, but I do think that will change," he told reporters. "As that changes, we'll see."