Joaquin Castro appears likely to challenge U.S. Sen. John Cornyn

U.S. Rep. Joaquin Castro listens to a speaker during a "Where Are The Children?" rally Thursday night highlighting the over 600 children that were separated from their parents while trying to immigrate to the United States. The rally took place on Guadalupe Plaza in San Antonio on May 31, 2018. Robin Jerstad for The Texas TribuneU.S. Rep. Joaquin Castro, appears likely to forgo re-election next year and instead challenge U.S. Sen. John Cornyn, R-Texas.According to a source close to Castro, whil