Justin Amash: The few times a member of Congress has left a political party in recent history

WASHINGTON – Rep. Justin Amash's announcement that he's leaving the Republican Party makes him part of a small group of members of Congress that have quit a party or changed parties altogether in recent history.

In an op-ed in the Washington Post published on July 4, Amash said that modern politics were "trapped in a partisan death spiral" and announced his resignation from the GOP to become an independent. Amash is the only Republican member of Congress to have declared his support for impeaching President Donald Trump.

After Amash's declaration of his political independence, Trump lashed out at the Michigan lawmaker, calling him "one of the dumbest & most disloyal" in Congress.

Changes in party affiliation are not unusual in American politics. Hillary Clinton once volunteered for Republican Barry Goldwater's 1964 presidential bid and was active in Republican politics as a Young Republican before becoming a Democrat. Teddy Roosevelt famously ran for president again in 1912 as a representative of the Bull Moose Party rather than run again as a Republican.

Amash's decision to change parties while in office, though, is unique.

"Amash is the first Republican House member in 20 years to leave the GOP," explained Antoine Yoshinaka, a political science professor at the New York State University at Buffalo and the author of a 2015 book on party switching.

Only three senators have changed parties while in office in the 21st century, according to the Senate's data. A USA TODAY analysis of Congress' biographical data shows that only five members of the House of Representatives have changed parties during the 21st century. After changing parties, most of the incumbents go on to lose re-election or retire from office.

Amash leaves the GOP: Justin Amash, sole Republican in Congress to support Trump impeachment, says he's now an independent

Trump responds: Trump lashes out at Justin Amash, calls him 'one of the dumbest & most disloyal' in Congress

Amash is only the third Republican to leave the party in the 21st century

Only two other Republican members of Congress have left the party since 2000. In 2001, Sen. Jim Jeffords of Vermont left the Republican Party over what he saw as a rightward shift in the party's platform, saying in a speech at the time that "I have changed my party label, but I have not changed my beliefs." Jeffords, like Amash, became an independent, though Jeffords caucused with the Democrats.

In 2009, Sen. Arlen Specter of Pennsylvania left the Republican Party to become a Democrat. He lost his bid for re-election in 2010 to Sen. Pat Toomey, who'd originally challenged Specter in the Republican primary.

Changing with political winds

Most of the members of the House of Representatives to switch parties while in office in the 21st century were southern Democrats who became Republicans as the political winds shifted and the South became redder. Parker Griffith, a member of Congress from Alabama, switched from the Democratic Party to the Republican Party in December 2009 amid the debate over the Affordable Care Act, also known as Obamacare. Griffith went on to lose the Republican primary to Mo Brooks.

"Amash is the first Republican House member in 20 years to leave the GOP," Yoshinaka said, noting that the last Republican member of the House to leave the party was New York congressman Michael Forbes, who switched from the Republican Party to the Democratic Party in 1999 and lost in the 2000 Democratic primary.

More: Senate passes $4.6 billion border funding bill amid gridlock on humanitarian funding

More: Trump says detention facilities 'beautifully run' after report describes dangerous conditions

Some members have switched parties multiple times

Rep. Virgil Goode, of Virginia, was re-elected in 2000 after switching from being a Democrat to an independent, and in 2002, when he switched to become a Republican. At the time of his first switch, he'd said that he wanted to be able to vote in line with his principles without pressure from a political party.

"You don't have some Democrats telling you didn't vote with the national party line enough," he said in January 2000, according to the Washington Post. "I will be voting as I have been in the past."

Goode lost re-election in 2008 to a Democrat, Tom Perriello.

More: Trump says he may issue executive order over citizenship question on 2020 census

Amash's future in the House is unclear

The House Republican Conference's rules are unclear on the question of what happens if a member of Congress leaves the party.

According to the rules, "All Republican Members of the House of Representatives...and other Members of the House as determined by the Republican Conference of the House of Representatives...shall be Members of the Conference."

A 2/3 vote of the entire Republican conference, or about 132 out of the 198 members of the conference, would be required to expel a member.

Additionally, Amash cannot be removed from his spot on the powerful House Oversight Committee without a resolution being passed by the full House of Representatives to do so, which would require some Democrats to vote in favor of the resolution.

Amash's electoral future is more uncertain, though. The Detroit Free Press noted that a large roster of Republicans had lined up to run against him in the Republican primary, and now that Amash has left the Republican Party, the race for his district becomes a three-way contest between the Republicans, Amash, and the Democrats.

Party switching isn't always the end of a political career, though.

Sen. Richard Shelby, R-Ala., who currently chairs the powerful Senate Appropriations Committee, was actually first elected as a Democrat in 1986 and changed to the Republican Party in 1994. He's won every election since then.

More: Like what you’re reading? Download the USA TODAY app for more

This article originally appeared on USA TODAY: Justin Amash: The few times a member of Congress has left a political party in recent history