WASHINGTON (Reuters) – President Joe Biden travels to Texas on Tuesday to highlight the exposure of U.S. service members to toxins in war zones that can later result in serious health problems, like the cancer that killed his son and for which he blames Iraqi burn pits. Accompanied by Secretary of Veterans Affairs Denis McDonough, Biden will visit a clinic for veterans in Fort Worth and receive a briefing from staff on services for veterans and challenges they face, the White House said. He will deliver remarks on the administration’s efforts to address the problem, including a proposed rule t…