Senate Republicans unveiled legislation that would replace Obamacare with a plan that scales back aid to the poor while killing a tax on the wealthy on Thursday. 

The bill's fate was quickly thrown into question as several senators voiced skepticism. 

Four conservative Republican lawmakers said they could not support the measure in its current form. Democrats are united in opposition. Republicans view Obamacare as a costly government intrusion into the private marketplace.

Meanwhile, shares of hospital companies and health insurers rose on the bill's release, with the overall S&P 500 healthcare sector closing up 1.1 percent at an all-time high.