After the undignified theatrics at Brett Kavanaugh’s confirmation hearings last week, it was hard to imagine that the opposition to this competent Supreme Court nominee could get any more embarrassing. Well, how about a campaign to trade a Senator’s vote for political donations?

A crowdfunding website is trying to strong-arm Senator Susan Collins, the Republican from Maine, by giving more than $1 million to her 2020 opponent—unless she opposes Judge Kavanaugh. Donors are asked to make a financial pledge and then enter their...