Ron Brownstein on the defiant red border states: A pregnant teenager writhing in pain as she suffered a miscarriage while trapped in the barbed wire that Texas has strung along miles of the state’s southern border. A 4-year-old girl collapsing from heat exhaustion after Texas National Guard members pushed her away from the wire as she tried to cross it with her family. Texas state troopers receiving orders from their superiors to deny water to migrants in triple-digit heat. Officers on another occasion ordering troopers to drive back into the Rio Grande a group of migrants, including children and babies, that they found huddling alongside a fence by the river. These are all incidents that a medic in the Texas Department of Public Safety says he witnessed during recent patrols, according to an explosive email published this week by the Houston Chronicle and the San Antonio Express-News. “I believe we have stepped over a line into the in humane [sic],” the medic, Nicholas Wingate, wrote in the email. These revelations capture not only the extreme tactics that Texas’s Republican governor, Greg Abbott, and state law-enforcement officials are employing against undocumented migrants seeking to cross the U.S. border with Mexico. They also show how aggressively Texas and other Republican-controlled states are maneuvering to seize control from President Joe Biden’s administration over immigration policy. To many immigration experts, these moves by Texas, like the harsh measures against undocumented migrants signed into law this spring by Florida Governor Ron DeSantis, push to the edge the legal limits on…