WASHINGTON — A U.S. senator threatened the NFL with legislation over Washington's nickname, a letter was dispatched to the other 31 team owners, and the issue was linked to the league's others recent troubles Tuesday as the anti-"Redskins" movement took its cause to Capitol Hill. In a news conference that featured Native American, civil rights and religious leaders, Sen. Maria Cantwell took aim at the NFL's pocketbook by announcing she will introduce a bill to strip the league's tax-exempt status because it has not taken action over the Redskins name. While prospects for such a bill becoming law would be tenuous, the inevitable hearings before lawmakers would enhance the spotlight on a movement that has gained substantial momentum over the last two years.