Washington: US President Donald Trump may have big policy plans for 2018, but political distractions are likely to shadow prospects of big legislative achievements.

White House officials say Trump wants to rein in the threat from North Korea and list four top domestic priorities on his 2018 agenda: Repealing and replacing President Obama's 2010 health care law, welfare reform, immigration, and a new infrastructure plan.

Yet the Republican-controlled Congress has been struggling to pass some of Trump's major priorities since his election - and their challenges will only increase in 2018. The GOP's Senate bare majority will shrink when Alabama's newly elected senator, Democrat Doug Jones, is sworn in.

In January, lawmakers will have to confront a thicket of unfinished business. In their rush to get home for the holidays, the GOP-led Congress passed a short-term spending bill that expires on January 19.

Trump and GOP leaders will have to negotiate a longer-term spending deal before then to avert a government shutdown, and they will likely need Democratic support for that to pass. Other sticky issues on the January agenda include legislation aimed at stabilising the Obamacare individual insurance markets and reauthorising the Foreign Intelligence Surveillance Act, a contentious anti-terrorism law that gives law enforcement sweeping spy powers.

What's more, lawmakers will be consumed with their own 2018 mid-term elections - and the increasingly contentious Russia investigations.

"As everybody in Washington knows, a midterm election year is a year when most legislation comes to a standstill," said David Cohen, a political science professor at the University of Akron.

"Members of Congress are going to be obsessed with winning re-election," Cohen said, and will be more eager to campaign at home than be in Washington casting tough votes.

Here are seven key issues that Trump and Congress will confront:

A North Korean Pukguksong-2 is launched at an undisclosed location on February 12, 2017. Photo: KCNA/AP

North Korea

Trump will lobby China - and other countries - to twist the economic screws on North Korea, in the hopes of forcing that rogue nation to give up their nuclear weapons program.

Trump travelled to Asia to press that issue in November and declared North Korea a state sponsor of terror. Yet North Korean leader Kim Jong-un has more or less thumbed his nose at the effort, recently setting off another ballistic missile test, and continued threatening the US and its allies.

As 2018 approaches, Trump and his advisers hope to settle the dispute diplomatically, but they have not ruled out the possibility of a military strike.

Trump wants to "transform" the nation's infrastructure, including highways and railways. Photo: AP

Infrastructure

In his 2018 budget proposal, Trump sought $US200 billion ($256 billion) over 10 years to spend on infrastructure, leveraging private-sector spending to focus federal dollars on "transformative" projects seen as priorities at both the federal and regional level.

That went nowhere in 2017, as Trump and the GOP-led Congress focused instead on trying to repeal Obamacare and enacting tax cuts. But the President plans to rev up that push early next year, with the hope that Democrats will cooperate.

Infrastructure spending is generally a bipartisan issue, and few dispute the need to improve the nation's highway and bridges. But Trump and Democrats have already outlined competing plans, and conservatives are likely to oppose any legislation that calls for massive new spending.

So the fate of that will likely depend on Trump's willingness to cut a deal with Democrats - and vice versa - heading into a heated election year.

Senate Majority Leader Mitch McConnell. Photo: Bloomberg

Healthcare

Trump insists he has not given up on his goal of repealing and replacing the Affordable Care Act, former president Obama's health reform law, even though Republicans in Congress could not muster enough votes to deliver on that long-promised goal this year.

After Congress passed a massive tax bill in December that included measures to repeal Obamacare's individual mandate, Trump declared the law was "essentially" repealed and lawmakers would work together to find a replacement. (However, the law is barely touched, though the requirement that nearly everyone have insurance or pay a penalty at tax time was repealed effective in 2019.)

Overhauling Obamacare will only get more complicated in 2018, as Republicans will have just 51 seats in the Senate. And the GOP's previous efforts to nix it sparked intense anger among voters who wanted to keep the coverage - something lawmakers may not want to reignite when many of them will be on the ballot.

Senate Majority Leader Mitch McConnell signalled little interest in taking another stab at the issue.

"Well, we obviously were unable to completely repeal and replace with a 52-48 Senate," McConnell told NPR in a December 21 interview. "We'll have to take a look at what that looks like with a 51-49 Senate. But I think we'll probably move on to other issues."

Other Republicans pushed back, saying the GOP should not give up on that long-touted campaign promise.

Democrats Nancy Pelosi and Chuck Schumer speak with Dreamers on Capitol Hill in September. Photo: AP

Immigration

Congress has a March deadline to decide the fate of the so-called Dreamers, the approximately 700,000 immigrants brought to the US illegally when they were children. Trump nixed an Obama-era program that shielded the Dreamers from deportation, but he also said Congress should figure out a legislative fix so the young people aren't sent back to countries they did not grow up in.

Critics have called the Obama protections - known as DACA, or Deferred Action for Childhood Arrivals - a form of "amnesty" and suggested those young immigrants have taken jobs from Americans. But there's bipartisan support in Congress and in the public to grant the Dreamers legal status and even a path to citizenship.

Whether Trump - who campaigned on a hardline anti-immigrant platform - will sign such a bill is unclear. He has sent mixed signals on the issue, and he's also called for new restrictions on refugees and others seeking entry into the United States.

After the December 12 arrest of a man who tried to set off a bomb in a New York commuter tunnel, Trump called for the end of "chain migration" and the diversity visa lottery programs. Those issues may again come up this year.

Republicans want to channel momentum from the GOP's victory on taxes into a push to overhaul the nation's welfare programs. Photo: Bloomberg

Welfare reform

In announcing a new major legislative priority following the tax cut bill, Trump said welfare reform was "desperately needed in our country".

A Trump budget proposal last year called for adding work requirements to some government programs and tightening eligibility requirements for low-income tax credits.

"We want to get our people off of welfare and back to work," Trump said. "So important. It's out of control. It's out of control."

Democrats say welfare reforms instituted two decades ago are working and that Trump wants to punch major holes in the social safety net.

A portrait of Donald Trump is set on fire by Iranians protesting his decision to recognise Jerusalem as capital of Israel. Photo: AP

Iran

Trump announced in October he would no longer certify that Iran is in compliance with an Obama-era deal, in which Tehran pledged to give up the means to make nuclear weapons while the US and allies ease economic sanctions. Instead, Trump called on Congress to improve the agreement, and the fate of the Iran nuclear deal is likely to come to a head in 2018.

Supporters of the agreement fear Iran will walk away from the deal and pursue nuclear weapons anyway, triggering a dangerous arms race in the Middle East. Trump is up against his own side on this issue, with Republican Senator Bob Corker, the current chairman of the Senate's Committee on Foreign Relations, keen to preserve the deal.

Steven Mnuchin, US Treasury secretary, is confident that the nation's debt ceiling will be raised before the northern summer. Photo: Bloomberg

The debt limit

The US Treasury will run out of money to pay its bills sometime in the northern spring - unless Congress and the President agree on legislation to raise the nation's debt limit. The Treasury Department lost its authority to borrow any new money to pay the government's obligations on December 9.

Officials are currently taking "extraordinary measures" to keep from defaulting on the government's current obligations, including Medicare benefits and the interest on the national debt. But the agency will run out of those accounting gimmicks in late March or early April, according to an analysis by the Congressional Budget Office.

That could lead to a round of partisan fiscal brinksmanship - with threats of defaulting on the government's debts. Conservatives have generally opposed increasing the nation's borrowing authority, so Trump will likely have to negotiate with Democrats to come to an agreement. Three Senate Democrats propose scrapping debt ceiling.

USA Today