A collection of 12 groups sent a letter to Congress Wednesday supporting the American Health Care Act, sending GOP leaders a lifeline as they try to deal with mounting opposition from conservatives and moderates to the plan to repeal and partially replace Obamacare.

What they say: The groups note that the bill is the first step to repealing the Affordable Care Act. "As advocates of free-market principles and limited government, we endorse this significant legislation," the letter said.

Who signed the letter: Most prominent among the groups is the Americans for Tax Reform, which is run by Grover Norquist. Norquist is a deficit hawk who calls on all Republicans to sign a pledge of no new taxes.

The other groups are the are the National Taxpayers Union, Association of Mature American Citizens, Center of the American Experiment, Citizens against Government Waste, Independent Women's Voice, Institute for Liberty, Log Cabin Republicans, Market Institute, Obamacare Repeal Coalition and the Small Business and Entrepreneurship Counsel.