When Eric Johnson made headlines last September for leaving the Democratic Party for the Republican Party, I sent him a text asking if he’d talk. Johnson, a Dallas native who served six terms in the Texas House before first getting elected mayor, in 2019, didn’t put me on his calendar then, and he later explained that he preferred to speak to national media rather than local and statewide outlets. But when I contacted him again this spring, he was eager to talk—and he didn’t hold back. (snip) TM: Last year you announced that you were switching your party affiliation from...