Arlen Specter left because he was losing as a Democrat in Pennsylvania. Decades later he switched back because he was losing as a Republican in Pennsylvania.
Michael Bloomberg left the Democrat part to run for mayor of New York City because the Democrat slate of candidates was full, so he switched to Republican to run. After he left office, he left the Republican party and became an Independent.
Joe Lieberman left the Democrat party because he lost his primary election in Connecticut with only a 10% turnout of Democrat voters. He switched to Independent to run in the general election and won reelection to the Senate.
Joe Manchin left the Democrat party because Chuck Schumer lied to him when he made a deal with Manchin regarding the inflation reduction act in exchange for Manchin's support for the CHIPS act. Schumer got the CHIPS act passed and then gutted the provisions of the inflation reduction act that Manchin wanted.
Kyrsten Sinema left the Democrat party over disgust at how she was treated by Schumer during the deal-making with Joe Manchin.
The only person I can recall who left the Democrat party over integrity is former Congressman Phil Gramm. Gramm was elected as a Democrat in 1978 and won reelection in 1980. After winning a third term in 1982, he was kicked off of House Budget Committee within days of starting the 1983 term, Gramm resigned from Congress. In the upcoming special election to fill the vacancy, Gramm registered as a Republican and ran to fill the seat he just vacated. He told Texans that he had too much respect for the voters to switch parties after being elected, so he resigned to give the voters a chance to send him back as a Republican. Gramm won the special election and finished his term before running for the Senate and winning. He served three terms in the Senate.
-PJ
“The only person I can recall who left the Democrat party over integrity is former Congressman Phil Gramm. Gramm was elected as a Democrat in 1978 and won reelection in 1980. After winning a third term in 1982, he was kicked off of House Budget Committee within days of starting the 1983 term, Gramm resigned from Congress. “
I stand corrected.... except for two Democrats I know of. Reagan is one and Trump, registered Democrat in 2001, is another.