Senator Majority Leader Mitch McConnell arrives at the U.S. Capitol on the day Senate Republican leaders unveiled a draft bill on health care in Washington, D.C. REUTERS/Kevin Lamarque

A seven-year push by U.S. Republicans to dismantle Obamacare and kill the taxes it imposed on the wealthy reached a critical phase on Thursday when Senate Republican leaders unveiled a draft bill they aim to put to a vote, possibly as early as next week.

With Democrats deeply opposed to Republican attempts to overhaul former President Barack Obama’s signature healthcare law, the route to passage was extremely narrow for President Donald Trump’s party, with no assurances that moderates and conservatives will be able to bridge their differences.

The draft bill proposes repealing a 3.8 percent net investment income tax on high earners retroactively to the start of 2017, not at some point in the future, as some analysts had speculated. The tax, affecting high-income Americans and imposed to help pay for Obamacare, has been a key target for Republicans.

Senate Majority Leader Mitch McConnell and his lieutenants worked in secret for weeks on the bill and he said debate on it would start next week.

Republicans who control the House of Representatives approved a more conservative version last month.