– The fate of a federal government shutdown is all up to Congress and ­President Donald Trump.

Republican and Democratic congressional leaders are optimistic that when they return from their recess the last week of this month, they'll reach a deal and avert a government shutdown by April 28, when legislation that is now funding the government expires.

Yet there are a number of issues, including the White House's push for a U.S.-Mexico border wall money and Trump's threat this week to pull some health care funding, that could lead to a ­blowup.

This year's showdown is most likely in the House, where Republicans are counting on Democratic support to pass a spending bill because some House conservatives have steadfastly refused to vote for spending bills.

That could, however, mean White House priorities go wanting, for now. Here's a look at the potential flash points:

Trump's wall

The administration is asking for $1.5 billion to start building a wall along the U.S. southern border. Candidate Trump promised that Mexico would pay for the wall, but the administration has since said U.S. tax dollars will finance it.

It's a nonstarter with Democrats: "They'll have to fight it out in their caucus," Sen. Bill Nelson of Florida said of the GOP. "This senator, this caucus, is not going to vote for money for a wall."

Health care bill

Trump this week threatened to withhold payments owed to health insurers under the Affordable Care Act as a gambit to force Democrats to the bargaining table.

Democratic leadership will insist that the budget package carries language to ensure the subsidies are paid. Democrats "will not negotiate with hostage takers," said Sen. Ron Wyden of Oregon, the top Democrat on the Senate Finance committee.

Coal miners

A dispute over health care benefits for retired coal miners nearly forced a government shutdown in December. Senate Democrats demanded a permanent extension, but House Republicans agreed to only four months.

Democrats reluctantly accepted the extension but have made it clear they intend to use whatever means they have to get a permanent fix. Senate Majority Leader Mitch McConnell is expected to play a decisive role.

'Poison pills'

These can take many forms, including efforts to defund Planned Parenthood or undermine the Consumer Financial Protection Bureau, established under Obama. Trump's budget director, Mick Mulvaney, is also reportedly asking lawmakers to include language that would curtail money for cities that do not enforce federal immigration policy.

Congressional Democrats say such partisan riders won't pass muster; advocacy groups say they're keeping watch.

"Congress is going to have only a few days to resolve" the must-pass legislation, said Robert Weissman, president of the nonpartisan group Public Citizen. "It's an opportunity for things to be done in the dark of night, to be done super quickly without adequate public scrutiny."

The unknowns

Or, there's always something. For instance, bad feelings linger over the "nuclear option," which Republicans triggered recently to eliminate the 60-vote filibuster threshold for Supreme Court nominees. Reaching a budget deal "was going to be hard already. This makes it even harder," said Sen. Chris Murphy, D-Conn., a member of the Senate Appropriations Committee.

It could work the other way, said Sen. Roy Blunt, R-Mo., a top Senate appropriator, who called the budget talks "an opportunity to come back together now and get something done and move forward."