The list is long, but for starters Mumia Abu-Jamal and Leonard Peltier are obvious cases, imprisoned since 1981 and 1977 respectively. The Black Panther and AIM had countless other political prisoners over the years. Since 2001, anti-terrorist laws have been used against eco-activists to imprison them.

There are prisoners of the social war in every country, but i think it's unique that a country has prisoners for life where they're accused of crimes that noone can prove and noone dares say they committed. In contrast, Georges Ibrahim-Abdallah (french political prisoner since 1984) or Abdullah Öcalan (turkish political prisoner since 1999) have both committed actual crimes and do not claim otherwise. To be clear, i will stand for their liberation too, but it's clear from the history of COINTELPRO (and related militant assassinations) that the US is not better than Saudi when it comes to thought crimes.

More recently, Chelsea Manning was a US political prisoner. And we can say that despite being incarcerated in the UK, Julian Assange is a US political prisoner to this day.

Some people argue that every prisoner is a political prisoner, since prisons are a recent invention and there's entire policies around how to fill them with desperate people to turn them into cheap labor for the industry. I won't make that point here, but it's worth keeping in mind when considering that the US has the highest incarceration rates in the world.

Most of the people (though not all) who are or were in prison for the events of January 6. Approximately 400 people give or take, though a number of them have already completed their sentences.

There’s a rich history of political incarceration in the United States beyond just this, particularly egregious example. The Wikipedia entry on the topic is fairly extensive