Yet Mr. Manchin’s unique ability to survive in West Virginia is the last vestige of the state’s once-reliable New Deal Democratic tradition, dating to old industrial-era fights over workers’ wages, rights and safety. It was one of the most reliably Democratic states of the second half of the 20th century, voting in defeat for Adlai Stevenson in 1952, Hubert Humphrey, Jimmy Carter in 1980 and Michael Dukakis. The so-called Republican “Southern strategy” yielded no inroads there... He might not have won the seat at all if he wasn’t a popular governor when he ran for the Senate in 2010. To win, he ran an advertisement promising to take “dead-aim” at the Obama-era “cap and trade” bill, which hobbled the party throughout coal country. The ad showed him shooting a copy of the legislation, which aimed to set limits on greenhouse gas emissions but created a market for companies that cut pollution quickly to sell allowances to high polluters. In 2018, Mr. Manchin may have only won re-election because of the favorable national environment that helped Democrats retake the House.