When Tennessee’s Republican governor, Bill Lee, dispatched his National Guard troops to Washington to support President Trump’s crackdown on crime, Democrats and other critics wondered why he didn’t keep them within state lines. Memphis, after all, has long been one of the most dangerous cities in the country, with a murder rate about twice as high as the nation’s capital, according to F.B.I. statistics. Nashville has a higher rate of violent crime than Washington as well. The same questions could be asked of other Republican governors like Greg Abbott in Texas, Mike DeWine in Ohio and Mike Kehoe in Missouri,...