The longest-serving Republican in the Iowa Legislature said he's leaving the party, in part because of his disapproval with President Donald Trump.

Rep. Andy McKean, who represents Anamosa in the state House of Representatives, announced Tuesday that he plans to register as a Democrat and vote with the minority caucus.

"With the 2020 presidential election looming on the horizon, I feel, as a Republican, that I need to be able to support the standard bearer of our party," McKean said during a news conference at the Capitol. "Unfortunately, that's something I'm unable to do."

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McKean said Trump is just one part of a bigger national trend of partisanship that made him feel out of place in the Republican caucus. McKean said when he joined the Iowa Statehouse 40 years ago, there were many moderates in the Republican Party. But now, he said, the ranks have thinned.

"I think the party has veered very sharply to the right," McKean said. "That concerns me."

House Minority Leader Todd Prichard, the top Democrat in the chamber, confirmed McKean's plans earlier Tuesday and joined him at the news conference.

"The Democratic party is a big tent, it's got a wide range of views and ideas," the Charles City lawmaker said. "We're pleased to have Andy's experience and ideas as part of our discussion when we go to caucus."

McKean had a "no party" affiliation on the Iowa Legislature website briefly Tuesday before updating it to reflect that he now identifies as a Democrat. According to the site, McKean has left his Republican committee assignments.

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McKean's exit will not change the Republican majority in the House, though it further shrinks it. Republicans will now have a 53-member majority in the 100-member chamber, down from 59 at the end of the last session, the result of several Republicans either retiring or losing their re-election bids in November.

While Republicans maintain a trifecta of control, McKean's move could make it easier for Democrats to retake control of the House in 2020.

The Democratic Legislative Campaign Committee, which helps elect Democrats, made note of that reality in a statement.

"Representative McKean didn't leave the Republican Party. The Republican Party left him — and their loss is our gain," said DLCC executive director Jessica Post. "We're going to have his back in 2020 — and with this seat in Democratic control, the path to taking back the Iowa House is clear."

The news had a mixed response from Iowa Republicans. House Speaker Linda Upmeyer, R-Clear Lake, said in a statement that she respected McKean's decision.

"This will not distract us from moving forward with the conservative agenda that Iowans have tasked us with," Upmeyer said. "As a majority of 53 strong Republicans, we are committed to completing our work and wrapping up the session.”

Jeff Kaufmann, chairman of the Republican Party of Iowa, was more critical. He indicated the party would fight for McKean's seat, which represents parts of eastern Iowa.

"When he was running for office a mere five months ago, he made a commitment to the voters of District 58, running on the Republican platform," Kaufmann said in a statement of McKean. "Today, he has violated the trust of the voters in his district."

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Prichard said the shift creates an "interesting dynamic" for the rest of the session, which is expected to end within days. It's unclear whether Republican lawmakers have the votes to pass several policy bills.

"If the majority wants to bring forward what I would call controversial and bad ideas ... it would probably delay," Prichard said. "We're not going to lay down and just acquiesce to that kind of partisan idea. ... It could definitely prolong the session."

McKean is not the first Iowa lawmaker to cite Trump as a reason for leaving the Republican Party. Former Sen. David Johnson quit the Republican Party in 2016 in protest of Trump's candidacy. Johnson, who later registered as an independent, did not seek re-election in 2018.

Former Rep. Dawn Pettengill, a Republican from Mount Auburn, left the Democratic Party in 2007. She did not seek re-election in 2018.

McKean, a retired attorney, has been long viewed as a moderate within his party and hasn't always voted along party lines. Earlier this session, he was the only Republican in a committee meeting to vote "no" against a bill that would revamp who is on the commission that selects judge nominations for the Iowa Supreme Court.

Many Republican lawmakers argue the legislation would make the nomination process more accountable to voters, but Democrats and lawmakers like McKean have said it will make the courts more partisan.

While McKean also considers himself a moderate, he said he still is more fiscally conservative. But he said he sees the Democratic caucus as more moderate, and that he will be able to find a role in the party.

"There may be some things I might not appreciate in that caucus as well," he said. "I will continue to speak out for what I believe in. I look forward to that opportunity."

McKean has been in the Iowa Legislature for decades, though he left for several years. He was first elected to the Iowa House of Representatives in 1978, and also served in the Iowa Senate from 1993 to 2003. He rejoined the House when he was elected to represent Anamosa in 2016.