(CNN)Sen. Susan Collins declined last week to back President Donald Trump for reelection, saying she would focus on her own race while suggesting that she only picked sides in 2016 because she was not on the ballot. "I was not up for reelection," the Maine Republican told reporters, referring to the 2016 race, when she publicly voiced her opposition to Trump's presidential campaign. "I didn't have my own race to worry about at that point." But a dozen years ago, as she was running for reelection, Collins endorsed Republican Sen. John McCain over then-Sen. Barack Obama. She served as a...