In the final weeks of 2019, a top fundraiser for Sen. Susan Collins walked into a perilous meeting at a Corner Bakery in Washington, D.C. For the first time in her two-decade Senate career, the Republican lawmaker from Maine was in danger of losing her seat. President Donald Trump’s dismal approval ratings were dragging her down in the polls, and she was falling behind her likely 2020 Democratic challenger in fundraising. Scott Reed, head of the Collins super PAC, was on a mission to close that gap. Reed was meeting that day with three executives from a Hawaiian defense contractor,...