HOUSTON (AP) — The three leading Democratic presidential candidates clashed over health care, immigration and President Barack Obama's legacy on Thursday in a fierce debate that pitted an aggressive Joe Biden against liberal rivals Elizabeth Warren and Bernie Sanders.

"This is America," said Biden, his party's early front-runner, before calling Sanders "a socialist." ''I stand with Barack Obama all eight years, good bad and indifferent."

The top White House hopefuls faced off for the first time alongside seven other candidates who are under increasing pressure to break out of the pack. All ass...