President Obama spoke during the Democratic National Convention in July.
Carolyn Kaster/Associated Press/File President Obama spoke during the Democratic National Convention in July.

WASHINGTON — The most powerful and ambitious Republican-led Congress in 20 years will convene Tuesday, with plans to leave its mark on virtually every facet of American life.

It plans to refashion the country’s social safety net, wipe out scores of labor and environmental regulations, and unravel some of the most significant policy prescriptions put forward by the Obama administration.

Even before President-elect Donald Trump is sworn in Jan. 20, giving their party full control of the government, Republicans plan quick action on several of their top priorities. Most notable is a measure to clear a path for repeal of the Affordable Care Act, although the repeal is not expected to take effect for years because Republicans are divided on how to replace the program.

Perhaps the first thing that will happen in the new Congress is the push for deregulation. Also up early: filling a long-vacant Supreme Court seat, which is sure to set off a pitched showdown, and starting confirmation hearings for Trump’s Cabinet nominees.

“It’s a big job to actually have responsibility and produce results,” said Senator Mitch McConnell of Kentucky, the majority leader. “And we intend to do it.”

But as Republicans plan to reserve the first 100 days of Congress for their more partisan goals, Democrats are preparing roadblocks.

The party’s brutal election-year wounds have been salted by evidence of Russian election interference, Trump’s hard-line Cabinet picks, and his taunting Twitter posts. (On Saturday, he offered New Year’s wishes “to all,” including “those who have fought me and lost so badly they just don’t know what to do.”)

Obstacles will also come from Republicans, who are divided on how to proceed with the health care law and a pledge to rewrite the tax code.

Some are also skittish about certain policy proposals, like vast changes to Medicare, that could prove unpopular among the broad electorate. And any burst of legislative action will come only if Congress can break free of its longstanding tendency toward gridlock.

For Republicans, the path to this moment has been long and transparently paved — the House in particular has signaled the Republican policy vision through bills it has been passing for years. But many of those measures have gathered dust in the Senate or been doused in veto ink.

The cleft between the two chambers recalls the situation faced by the insurgent House Republican majority in the mid-1990s. Speaker Newt Gingrich took control with a…