If we look at the population of the US at large, as of time of writing, 84.7% of Democrats, 43.0% of Independents, and 9.4% of Republicans support impeachment. Meanwhile, in Congress, literally 100% of Democrats support impeachment, and literally 0% of Republicans do. If we assume that the national values are representative, then the odds of all 133 Democrats who've expressed an opinion landing on the side of impeachment is extremely low, in the range of 0.000000003%, and yet here we are.
Why are the Democrats & Republicans in the House so homogeneous? Statistically it's extremely unlikely to get this 100% support/oppose, yet that's what has happened.
Things I can think of:
- The Democrats & Republicans in the House aren't representative of the population. If so, why? It seems weird too: it means the elected leaders don't actually represent the population, which seems to run contrary to the whole point of democracy.
- The Democrats who oppose impeachment and the Republicans who support it are in the "no response yet" column. However, it's unclear to me why this would make a big difference - presumably some of the US population polled don't respond either.
- They are under threat by their party to either vote along the party line or be expelled from the party. This is conceivable, but seems unlikely, because when Boris Johnson expelled rebels from his Conservative party a few months ago, 1) there were public warnings that he would do so and 2) it didn't stop the rebels from voting against his proposal. I haven't seen public warnings by either the Democrats or the Republicans, but it seems nobody wants to rebel anyway.
- They might not agree with/oppose impeachment on a personal level, but they are voting the other way because they believe that's what the people that voted for them want. It's conceivable, but there's no evidence for this in the New York Times list - the closest is Republican Michael Guest who said "I will not vote to silence the voices of over 700,000 Mississippians who voted for our president", but he didn't express a personal opinion. Update: there're now news items claiming that even vulnerable Democrats are supporting the impeachment, which seems to refute this as an explanation.