President-elect Donald Trump has promised to bring jobs back from overseas, destroy ISIS terrorists and build a wall on the Southern U.S. border with Mexico.

He has the advantage of a Republican-controlled Congress eager to put its imprint on foreign and domestic policy after eight years of President Barack Obama, and an engaged base of new GOP voters eager to shake up Washington.

But Democrats have vowed to block Trump’s agenda, including efforts to repeal and replace the Affordable Care Act.

And a rapidly changing geopolitical landscape threatens to upend Trump’s foreign policy goals.

Following are key issues Trump is likely to face:

Health care

Trump wants to repeal the ACA, known as Obamacare, and replace it “essentially simultaneously.” House and Senate Republicans last week began the repeal process, passing budget resolutions that allow lawmakers to gut the bill without the threat of a Democratic filibuster.

While most Republicans back repeal, citing rising premiums and strict federal mandates, there is no consensus on replacing Obamacare.

Congress can move quickly to repeal aspects of the law focused on taxes and spending. Other parts of the law, such as mandating insurance companies cover individuals with pre-existing conditions, could prove more complicated.

Some top GOP lawmakers have urged the incoming administration to slow down the repeal until a new health insurance program is ready to be implemented. But Trump, eager for an early political victory, has urged lawmakers to act quickly to undo the law.

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Senate Minority Leader Chuck Schumer (D-N.Y.) said Democrats will not help pass new legislation if Republicans leave millions of Americans without health insurance.

The economy

Trump has pledged to bring back manufacturing jobs, roll back regulations, rework international trade agreements and slash corporate and income tax rates.

Trump has promised to renegotiate the North American Free Trade Agreement, abandon the Trans-Pacific Partnership and impose a 35 percent tariff on imports from China and Mexico.

Mark Zandi, chief economist at Moody’s Analytics, said Trump’s strategy has caused a “a high level of uncertainty” in the business community. “I expect a lot of volatility,” he said.

Trump also has promised middle-class tax relief that would cut rates on businesses and individuals.

Economists say that while most households would see tax cuts under Trump’s plan, the largest benefits would go to high income earners.

The average tax bill in 2017 would fall by $2,940, but households with incomes over $3.7 million would receive an average cut of $1.1 million, the nonpartisan Tax Policy Center said.

National security

Trump says he will move away from reliance on “soft power” employed by diplomats for decades to avoid international disputes toward a transactional strategy reliant on deal making.

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Trump has indicated a desire to work with Russia to defeat the Islamic State terrorist group — despite the conclusions of the U.S. intelligence community that the Kremlin orchestrated cyberattacks to influence the presidential campaign.

Trump has called the post-World War II NATO defense alliance “obsolete” and said other nations were failing to meet military spending commitments.

Other provocative stances include plans to relocate the U.S. Embassy in Israel from Tel Aviv to Jerusalem. Trump also says the “One China” policy is “under negotiation,” hinting at a preference for Taiwan.

“He’s going to do the opposite of what is conventional wisdom in foreign policy,” said Jeremi Suri, a professor of global leadership and public policy at the University of Texas at Austin.

Trump says he will seek to rebuild the U.S. military to “crush and destroy” ISIS. He would boost the number of “combat ready” Army troops by 50,000, add 74 Navy ships and submarines and 87 Air Force fighter aircraft and develop a state-of-the-art missile defense system.

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The plan, experts said, could face resistance from deficit-conscious Republicans.

Immigration

Trump has signaled a hard line on illegal immigration, saying he will deport millions with criminal records and build a wall along the Southern border that Mexico will pay for.

During the campaign, Trump promised to create a deportation force capable of removing 11 million people who are in the country illegally. Trump has since adjusted his rhetoric and now says he will target for deportation more than 2 million immigrants with criminal records.

In a speech in August, Trump said his “enforcement priorities will include removing criminals, gang members, security threats, visa overstays, public charges . . . along with millions of recent illegal arrivals and overstays.”

The status of an estimated 750,000 immigrants brought to the United States illegally as children remains unclear.

A 2012 Obama executive order gave those immigrants, known as “Dreamers,” an opportunity to work in the country legally. Trump said he would revoke the order but indicated recently that he would work with congressional Republicans on a compromise “that’s going to make people happy and proud.”

Schumer says the only way to fix the nation’s “broken immigration system and secure our borders is to implement the bipartisan comprehensive immigration reform.”

Trump’s signature immigration policy during the campaign — building a wall along the Southern border funded by Mexico — has undergone some tweaking.

Trump now says the federal government will pay for the wall and Mexico would reimburse the costs later. It remains unclear how he would force Mexico to pay. Mexican officials say they will not fund the project.

Education

Trump is expected to push for expanded school choice and taxpayer-funded vouchers that allow students at poorly performing public schools to attend private schools. Public school advocates and teacher unions are expected to mount opposition.

Education secretary nominee Betsy DeVos told a Senate committee Tuesday she “is a strong advocate for great public schools” but “parents no longer believe that a one-size-fits-all model of learning fits the needs of every child.”

Union leader Randi Weingarten, head of the 1.6-million-member American Federation of Teachers, told the National Press Club this month that DeVos was the “most anti-public-education nominee in the history of the department.”

Trump, who has suggested the Education Department can be “largely eliminated,” says school choice policy should cover private, public, magnet and charter schools.

He has proposed using $20 billion in federal funds to establish block grants for states to cover 11 million students “living in absolute poverty.” The plan would allow students to receive $12,000 in “school choice funds,” if states also provided a combined $110 billion from their education budgets.