By Lisa Mascaro, Los Angeles Times.

Republican-controlled Congress opens Tuesday with the most sweeping conservative agenda in decades, providing Donald Trump ample room to gut the Affordable Care Act, slash corporate tax rates and undo Obama-era environmental regulations.

The House is almost certain to reelect Speaker Paul D. Ryan (R-Wis.) as its first order of business, dispensing with the messy political infighting that has hobbled Republicans in the past.

And the Senate will swiftly begin vetting the president-elect’s most controversial Cabinet picks, ready to confirm some when Trump is inaugurated as president on Jan. 20.

Yet Republicans remain at odds on some high-profile issues — such as how aggressively to investigate Russian hacking in the 2016 election — and how to fulfill other big-ticket promises, such as replacing Obamacare.

A forgotten mortgage stimulus program that was passed by Obama to help the middle class Americans reduce their monthly payments by as much as $4,264 each year.

Despite firm Republican control of both the White House and Congress, the internal disputes have left them without a clear plan yet for Trump’s first 100 days, or an endgame for the two years of the 115th Congress.

Trump’s often shifting views on major issues will test relations with GOP’s leaders on Capitol Hill, and his willingness to skirt ideological rigidity gives incoming Senate Democratic leader Charles Schumer of New York and House Minority Leader Nancy Pelosi of San Francisco an opening to influence and shape the president’s evolving agenda.

President Obama will visit Capitol Hill on Wednesday to meet with Democrats bracing for their new role, not just as the minority party, but as the main roadblock preventing Trump from dismantling the healthcare law and other parts of the Obama agenda.