I was 16 when George W. Bush won his first term in 2000, but had I been two years older, I would have voted for him.
I went to a very liberal university where everyone hated Bush and Iraq War protests happened almost daily, but I secretly still supported Bush in 2004. When I finished college in 2006, the Democrats took control of Congress, and I was actually kind of sad about that.
What happened? It may have started in 2007 when I took a trip to London. I hung out in a lot of pubs, and of course when people found out I was American, they wanted to vicariously take the piss out of George W. Bush by talking politics incessantly when all I wanted to do was drink pints and learn more about the Premier League.
By that point I was pretty anti-war. But another thing constantly came up: "So in America, you can't just visit a doctor for free?" And I would answer, "You can always go to the hospital, but if you don't have insurance you'll have to pay a large bill." I don't think a lot of younger Brits really understood the U.S. healthcare system, and they were completely dumbfounded by it. The conversation would always lead to, "Why wouldn't you just give everyone healthcare coverage?"
And I had no answer for that. It got me thinking independently about politics for maybe the first time. So the next year, when the Obama vs. McCain election came around, and Obama's platform was based around setting up a universal healthcare system, while right-wing commentary was vehemently opposed to the entire idea, citing the spectacular "failures" of such systems in Canada and the U.K., I began to lean hard left. Republicans were calling nationalized healthcare systems "failures" and "socialist systems." But I had been to the U.K., and not only were they most definitely not socialists, but their healthcare system wasn't a failure at all.
From there, I gradually became what's called a liberal in America as I realized that 21st century-era Republican arguments didn't stand up to the slightest bit of scrutiny.