WASHINGTON (Reuters) - U.S. Senator Jeff Flake said on Tuesday that Republican nominee Donald Trump will not be able to win the presidential election, and should not win it, if he maintains the positions that he holds now, including his harsh stance on immigration.

Republican U.S. presidential nominee Donald Trump speaks to the Trask Coliseum at University of North Carolina in Wilmington, North Carolina, U.S., August 9, 2016. REUTERS/Eric Thayer

In an interview, Flake said he still hopes Trump will change enough that the Republican senator from Arizona will be able to vote for the candidate in the Nov. 8 election.

But, Flake said, “It’s a slim hope.”

He said that as things stand, Trump will even have difficulty clinching the state of Arizona if the nominee, who has called for building a wall on the border with Mexico, does not develop a more “serious” immigration policy.

Arizona last voted for a Democratic presidential candidate two decades ago.

“Given the positions that he’s taken, if he continues to maintain those positions, if he continues to hold to the statements he has made, I don’t think he can win the presidency, nor do I think he should if he is unwilling to change,” Flake said of Trump.

“There is a big difference between winning a primary, getting what, 14 million votes, and getting 65 million votes that you’re going to need to win the presidency. In between those two numbers you encounter a number of swing voters, independents, who simply don’t cotton to the kind of message that he has been delivering. And that’s just the reality,” Flake said.

Flake, 53, has long been one of Trump’s more vocal critics on Capitol Hill. Trump’s inflammatory remarks about immigrants have been a particular problem for Flake, whose Southwestern border state has a large Hispanic population. Flake was among eight senators who proposed comprehensive immigration reform in 2013.

Flake memorably told a reporter last month that he would not be attending the Republican convention to nominate Trump because he had to mow the lawn.

Flake told Vanity Fair magazine in July: “I don’t think that there’s much worry of a Trump presidency if he doesn’t change.”

But he also insists that he will not vote for the Democratic candidate, former Secretary of State Hillary Clinton.

Flake, a member of the House of Representatives for 12 years before being elected to the Senate in 2012, said Arizonans are more realistic and pragmatic on immigration than Trump.

Right now, Flake said, Arizona is almost a “toss-up” in the presidential election.

Flake does not have to run for re-election to the Senate until 2018. His fellow Arizona senator, John McCain, is up for re-election this year, and faces both primary and general election challengers. McCain has said he backs Trump.

Flake said he respected Senator Susan Collins of Maine, another Republican, who said in an opinion article published on Monday that she definitely would not vote for Trump. Flake said he was not prepared to follow Collins’ example, which did not set off a stampede of Trump repudiations.