But it's happened only once, more than 200 years ago, and he was acquitted.

that's an impeachable offense under Article II, Section 4 of the Constitution. Just being a conservative judge who gets appointed by a conservative president isn't an impeachable offense, defined as "treason, bribery or other high crimes and misdemeanors." Only one supreme court justice has ever been impeached, and that was more than 200 years ago - and he was acquitted in the Senate by a large margin. Even the Democrats on the House Judiciary Committee wouldn't touch that - they're mostly lawyers so they know better. And, even if the mere fact of being appointed could be considered an impeachable offense, and articles of impeachment made it out of the committee, they'd have to be approved by the full House. Then, actual removal from office requires a 2/3 vote of the full Senate. None of these events are even slightly probable, even with more Democrats in Congress. So, running for for any office on the promise that the candidate will vote to impeach a SCOTUS appointment who hasn't committed any offense beyond being unsuitably conservative when that's an impossible promise to keep doesn't seem like a very good idea.

Always shoot to kill if you're going to shoot at all.

The next best is because it would definitely be a losing issue to run on.

It's time to do what Republicans do all the time: take something that everyone assumes is off limits and start normalizing it. We should do nothing but talk about packing the court until 95% of Democrats think it is a good idea.