Are there any notable American politicians who switched from liberal to conservative or vice versa?

No. From memory, he applied to join, but abandoned his application when told he would have to undertake not to employ Catholics as well as not to employ Blacks.

Some think that the public’s (and the politicians’) view of the political spectrum has shifted to the right quite a lot, so that all the candidates who were once called moderate are now called left, many who were called left are now ignored for being too far left, and many who were ignored for being too far right are now getting some attention.

That is just to show that the classifications are not reliable in trying to figure out where anyone stands, because the goalposts keep moving.

It’s worth pointing out that the general political foundations of the US have changed considerably over the last 50 years and probably at an increasing pace approaching the present day. Neither party is an especially “big tent” at the moment, though the Democrats are probably more so. The question of “ideology” changing is therefore a tricky one–one might be at and remain at the most “centrist” position of one party, or one might find it more congenial or more likely politically useful to change labels. I believe there is evidence to show that party-switchers do move more towards the ideology of the new party though I don’t have a cite.

Off the top of my head as party switchers not mentioned above:

-John Lindsay, Republican Congressman and Mayor of NYC who ran for the Democratic nomination for president in 1972.
-Alabama Senator Richard Shelby, who first won election as a Democrat and switched to Republican in 1994.
-Former Vermont Senator Jim Jeffords, elected as a Republican who switched to independent in 2001 and caucused with the Democrats.
-Lincoln Chafee of Rhode Island, a Republican Senator who later (out of office) became a Democrat and ran for the Dem nomination for presidency.
-Arlen Specter, former Senator from Pennsylvania, who was elected as a Democrat, switched to Republican, then switched back to Democrat.
–Most recently AFAIK, Jim Justice of West Virginia switched from Republican to Democrat in 2015, was elected governor, and just switched back to Republican.

Michael Bloomberg went from Democrat to Republican to Independent to Democrat again in less than 15 years. He endorsed for President George W Bush twice, followed up by Barack Obama and then Hillary Clinton.

There’s an entire Wikipedia article that lists the notable cases: Party switching in the United States

Hillary Rodham was president of the Wellesley Young Republicans her first year at that school. This was, obviously, before she became Hillary Rodham Clinton.

Parties does not enter into a lot of this. E.g., in the South a lot of long term conservative Democrats switched to being conservative Republicans, esp. in the 1980s.

The Neocons, OTOH, are definitely a group of liberal->conservative folk with a Wikipedia article.

Warren’s positions on numerous issues today are not that distant from those of the pre-“Contract With America” Republicans who were essentially wiped off the map by Gringrich-led neocons in the mid- ‘Nineties. The Republican party used to stand for civil rights, respect for the value of science and education, and pragmatism in government finance and economics. Even abortion rights, now a highly devisive party-line issue, was not previously a defining position. Now the Republican party has essentially been co-oped by corporate interests actively working to undermine democratic institutions and eliminate regulatory oversight, and Warren, who would have once been viewed as a ‘moderate’ fiscal conservative is now characterized as a radical leftist just barely more toward the center than Bernie Sanders, which tells you everything you need to know about how skewed the political landscape is.

Stranger

Robert Byrd, as mentioned upthread, is the best example I can think of. He genuinely repented from supporting racist policies to being supportive of civil rights. If I remember correctly he was frequently bashed by those on the right for being a flip flopper. I think that just goes to show he did have a genuine change of heart and that those on the right no longer felt he was one of them.

Although I suspect he was always a closet liberal, Wayne Morse was first elected to the Senate from Oregon as a Republican. Oregon was as solidly Republican as it gets in those days (around 1950). Two years later, he declared himself Independent and two years after he that he announced himself as a Democrat and won reelection as a Dem. He nearly single-handedly turned the State Democrat (with a lot of help from Richard and later Maureen Neuberger).

Lyndon Johnson was a fairly typical southern Dem who consistently resisted civil rights legislation as a senator, but as president he brought in very strong civil rights. He is said to have commented at the time, that he had pushed the south towards the Republicans for a generation. He was wrong; it is now two and heading for a third generation.

I’m curious as to why you don’t see him as a politician. He has run for President multiple times (in addition to his successful 2016 campaign, he ran in 2000 under the Reform Parry ticket). So how many times does one have to run for the highest political office in the country before they become a politician in your eyes? I think he is certainly a politician, simply a bad one (notwithstanding him winning the Presidency).

Technically, he actually did join. The KKK was a big political force of the time, and an advisor told him to join to get their votes. He paid $5 to join. They came to him a few days later and insisted he not hire any Jews or Catholics. Truman quit as soon as he heard that and got his $5 back.

She only became Hillary Rodham Clinton years after she was married, and Bill ran for Governor and she was criticized for not taking his name.

Senate Majority Leader Mitch McConnell deserves a mention. During the 1970s he was pro-choice, pro-union, in favor of the civil rights movement and the Equal Rights Amendment. He advocated campaign finance reform.

Then he saw how well Reagan did in his home state and never looked back.

During the 1990s he earned quite respect and relief among his Republican colleagues by openly opposing campaign finance reform.

In the current congress Kirsten Gillibrand of New York was a moderate to conservative congressman who campaigned against illegal immigration, for gun rights, and voted against the Obama stimulus package. She was then elected to the Senate and is now the 5th most liberal Senator.

There is one wild-eyed theory out there that most politicians are just blank pages which their donors write on, so that these “changes of heart” are merely the changing economic winds of their donors.

There is also the aspect of which party gets you elected more, and are you facing a primary challenge.

From what I remember, 538 did a study of Arlen Specter. When he was facing a primary from the right he moved right on the issues. When he was facing a primary from the left he moved left.

Hillary Clinton moved to the left to fend off a primary challenge from Bernie Sanders.

basically that is what politicians truly care about. Getting re-elected. Whether that comes from losing a primary or general election, or losing funding, they’ll vote accordingly.

Sir Winston Churchill was an honorary American, wasn’t he? Having been both a Liberal and a Conservative during his career.

I agree with the last sentence, but I think the endposts have shifted to the left a lot, not to the right.

The primary basis for Warren’s progressive credentials is her anti-big business stances, which would have been very much out-of-step with the Republican mainstream in any recent era.

I would guess he probably did have a change of heart on these issues (along with much of the rest of the country). But I don’t think what you said proves it. At the time he changed, being a flip flopper was far far less damaging to his political career than being a racist.

He’s also alleged to have thought he could earn the votes of black people for 200 years. He’s about 1/4 of the way there and going strong.

As a member of the House, Gillibrand represented a district in upstate NY, which is a conservative area. As a senator, she represents the entire NY state, which is much more liberal. As a politician with national aspirations, she has her eyes on the Democratic primary electorate, which is much more liberal yet.

As to the OP, I’m not sure if you would count journalist/activists for this purpose, but if so I would nominate David Brock. Former right wing hack, current left wing hack.

Also, while Ramsey Clark was a progressive Democrat when serving as AG under LBJ, at that time he was very much in the mainstream, while he moved into the radical left after leaving office.