Sen. Elizabeth Warren, D-Mass., plans to campaign for Iowa Senate candidate Zach Wahls this month, adding firepower to a raging battle between progressive outsider candidates and the Democratic Party establishment. Wahls, a state senator, is pitted against state Rep. Josh Turek, whom many perceive as the favorite of Democratic leaders in Washington, in the June 2 primary. The winner will take on Republican Rep. Ashley Hinson in what promises to be a closely watched race in the fight for control of the Senate. "Zach Wahls is running to shake things up," Warren said in a statement announcing her May 10 visit to a Wahls rally in Des Moines.…