The U.S. Senate on Thursday took a first concrete step toward dismantling Obamacare, voting to instruct key committees to draft legislation repealing President Barack Obama’s signature health insurance program.

The resolution passed  on Thursday by a a 51-48 vote and now goes to the House of Representatives, which is expected to vote on it this week. Scrapping Obamacare is a top priority for Republican President-elect Donald Trump and the Republican majorities in both chambers.

Republicans have said the process of repealing Obamacare could take months, and developing a replacement plan could take longer. But they are under pressure from Trump to act fast after he said on Wednesday that the repeal and replacement should happen “essentially simultaneously.”

Some 20 million previously uninsured Americans gained health coverage through the Affordable Care Act, as Obamacare is officially called. Coverage was extended by expanding Medicaid and through online exchanges where consumers can receive income-based subsidies.

Republicans have launched repeated legal and legislative efforts to unravel the law, criticizing it as government overreach. They say they want to replace it by giving states, not the federal government, more control.

House Speaker Paul Ryan said this week he wants to pack as many replacement provisions as possible into the legislation repealing Obamacare. But Senate Finance Committee Chairman Orrin Hatch, also a Republican, said that could be difficult under Senate rules.

The resolution approved Thursday instructs committees of the House and Senate to draft repeal legislation by January 27. Both chambers will then need to approve the resulting legislation before any repeal goes into effect.

Senate Republicans are using special budget procedures that allow them to repeal Obamacare by a simple majority so that they will not need Democratic votes. Republicans have 52 votes in the 100-seat Senate. One Republican, Senator Rand Paul, voted no on Thursday.

On Wednesday, Trump said he would submit a replacement plan as soon as his nominee to lead the Health and Human Services Department, Representative Tom Price, is approved by the Senate. Trump gave no details.

Democrats passed the Affordable Care Act in 2010 over united Republican opposition. Democrats say the act is insuring more Americans and helping to slow the growth in healthcare spending. But Republicans say the system is not working. The average Obamacare premium is set to rise 25 percent in 2017, according to Reuters.