Nonpartisan analysts say Democrats stand a good chance of winning the US House of Representatives and possibly the Senate in the November 3 midterm elections, which would give them a slice of power in Washington after two years of Republican control.
Democrats argue that Republicans have allowed President Donald Trump's administration to declare war and control spending, even though the US Constitution reserves those powers for lawmakers.
Here are some ways a Democratic Congress could hem in Trump's foreign policy.
Curb the Iran war
Trump did not secure approval from Congress before he launched the war with Iran on February 28, and Democrats have voted repeatedly to end the fighting unless he does so. One of these resolutions passed with support from a handful of Republicans, but Trump's administration ignored it.
With control of the House or the Senate, Democrats could cut defense spending to pressure Trump to obtain permission from Congress to continue the war. They could also require administration officials to testify publicly about their plans.
Fresh support for Ukraine
Trump has largely halted direct US financial and military aid to Ukraine, despite broad support from Democratic and Republican lawmakers as it fights a Russian invasion.
Most recently, he has angered members of Congress, including many Republicans, by lifting sanctions on Russian diesel and waiving sanctions on Russian energy only weeks after signing them into law.
With a victory in both chambers in November, Democrats would be able to decide what gets voted on and when.
That could allow them to approve new aid to Ukraine, which likely would pass with the two-thirds majorities needed to overcome a Trump veto.
They could also target other Trump activities. For example, Representative Gregory Meeks of New York, who could head the House Foreign Affairs Committee if Democrats win control, has introduced bipartisan legislation to block Trump's plan to bring Russian diesel back into the global market.
End military aid to Israel
Support for Israel has plummeted among Democrats over its conduct in the Gaza war, which has killed tens of thousands of Palestinian civilians. The ongoing violence in the Israeli-occupied West Bank and Israeli Prime Minister Benjamin Netanyahu's close alliance with Republicans have also been factors.
Democrats could limit or end military aid to Israel, which amounted to $3.8 billion in the most recent fiscal year. That is more than was provided to any other country.
Nearly half of House Democrats voted this summer to cut off aid to Israel. Some of those who voted against that effort, such as Meeks, have backed limits on providing weapons like heavy bombs to Israel.
Limit military spending and restore foreign aid
Democrats are far more likely than Trump's Republicans to limit military spending. Trump asked for an unprecedented 67% increase in the military budget this year, to $1.5 trillion, but Democrats blocked it in the Senate, citing his refusal to consult Congress about the Iran war and his steep cuts to social programs.
Trump has also withheld or canceled billions of dollars in foreign aid approved by Congress. Many Democrats have been angered by the cuts and say they will try to restore funding.