Doctors seen during a procedure. Wikimedia Commons Reactions have streamed in since House Republicans on Monday introduced their bill designed to replace Obamacare.

Titled the American Health Care Act, the bill aims to repeal and replace the Affordable Care Act, overhauling the healthcare system.

The bill tries to preserve some of the well-regarded aspects of the ACA, such as allowing people with preexisting conditions to keep their coverage — so long as they don't have a lapse in insurance.

At the same time, some estimates say millions of Americans could lose their insurance under the AHCA. And the AHCA is already facing backlash from conservative Republicans who have nicknamed the bill "Obamacare 2.0."

Since Tuesday, more than half a dozen doctors' organizations, hospital groups, and patient advocacy groups also do not seem to be the biggest fans of the bill in its current form. Here's what some of the major groups have said.