"Interview over. I don’t trust you anymore,” Sen. Martha McSally jokes as we’re getting ready to talk and I disclose that I’m not a dog person. Last November, McSally’s dog Boomer sat beside her on a couch as she conceded her 2018 Senate race to her Democratic opponent, now-Sen. Kyrsten Sinema. Ten months later, I’m meeting with McSally as she sits on a couch with a staffer’s white English golden retriever at her side. This time, she’s in her Senate office. McSally took a circuitous path to the upper chamber, having lost a bitter race against Sinema, only to be appointed to the Senate weeks later when Jon Kyl, one of McSally’s mentors, stepped aside. Without much time to settle into her new role, she is already having to prepare for another election in 2020, in a race that she recognizes is “ground zero for the Senate majority and the firewall in the direction of our country.” This is not an overstatement. Democratic presidential candidates are in a policy bidding war that has involved proposals to socialize health insurance and offer coverage to illegal immigrants, provide free housing, cancel student loans, and hand out monthly $1,000 checks, among other promises. Even if Democrats retake the White House, however, they will not be able to achieve a smidgen of their transformational agenda without control of the Senate. And they won’t win the Senate without beating McSally....