‘If a person is not a liberal when he is 20, he has no heart; if he is not a conservative when he is 40, he has no head.” No one is sure who said that (it’s sometimes erroneously attributed to Churchill, like everything else), but everyone is familiar with the sentiment: we are supposed to get more conservative as we age.

Elizabeth Warren didn’t get that memo. The 69-year-old Democrat and US presidential hopeful was a free-market-loving Republican when she was younger, described by old friends as a “diehard conservative”. Now Warren isn’t only a Democrat – she is one of the most progressive voices in US politics, with a similar ideological stance to Bernie Sanders. Indeed, Warren may be heading even further to the left than Sanders. On Monday, she proposed a plan to forgive $50,000 (£38,000) of student loans for people earning less than $100,000 a year, with the money coming from a new wealth tax. Warren also proposed an ambitious plan for free higher education, which she described as “bigger” than Sanders’ free college bill.

Warren has explained that she joined the Republican party because she believed in its conservative approach to markets. She left the party in 1996, she has said, because it started siding more with Wall Street, tilting the playing field against the little guy. While she has discussed her political journey in some interviews, it’s not something she has been keen to advertise, which is understandable: inconsistency isn’t seen as a good thing and we tend to look upon politicians who change their views with suspicion.

There is a big difference, however, between thoughtfully changing your mind and opportunistic flip-flopping. It would behoove many politicians to do a lot more of the former and less of the latter. After all: “If a person doesn’t change his mind when the facts change, he has no brain.” I believe it was Churchill who said that.