WASHINGTON -- For the past two years, U.S. foreign policy has been roiled by Donald Trump's presidency as he questioned long-standing tenets of Washington's alliances and relationships.

Now it's about be roiled yet again, as Democrats, having won control of the lower chamber of Congress, the House of Representatives, are poised to wield more influence on foreign and domestic policy.

The way the U.S. political system is structured, the executive branch -- the White House -- is dominant where U.S. foreign policy is concerned.

But congressional legislators have the most influence where money is concerned, controlling the budget strings to fund war, diplomacy, and intelligence operations, among other things.

Democrats in the House will be able to determine what bills can be considered in the chamber, and will have a bigger role in setting spending policy and writing legislation. That may include harder positions on Russia, Saudi Arabia, and elsewhere.

To be sure, the Democrats' victory in the House is counterbalanced by the Republicans' hold on the Senate, a hold that only tightened with the outcome of the November 6 vote.

At the very least, according to Marvin Kalb, a research fellow at the Brookings Institute and a former foreign correspondent, it may mean more confusion, and less coherence for foreign policy.

"There will be a great deal of talking, a great deal more of investigations, and meetings. But the more you have of those, the less chance there is of a formulated, counterargument, or counter-strategy that could be suggested to the president," he said.

David Wade, a former chief of staff to Secretary of State John Kerry, said in a commentary published before the vote that Democrats will have to lay out a vision of their own.

"The Democrats will have to define a foreign policy...navigating thorny issues that include articulating an alternative to Trumpism globally while still reconnecting with persuadable Trump voters who feel left behind by globalization," he wrote.

Ian Bond, who served as ambassador to Russia, NATO, and other posts in the British Foreign Ministry, said the U.S. midterms are seen in Europe as indicator of where Washington is headed.

Those in London in Brussels who believe in the decades-old transatlantic relationship between Europe and North America are hoping that the midterms produce a Congress that values America's European allies and puts some limits on President Trump's ability to disrupt the transatlantic partnership," he said.

Here's a look at some foreign-policy issues that may or not shift in the new Congress.

​RUSSIA

Under Republican control, the two chambers of Congress had largely been united on the question of Russia going back to 2014, when Moscow annexed Ukraine's Crimea Peninsula and fomented separatism in eastern Ukraine.

The 2017 Countering America's Adversaries Through Sanctions bill, or CAATSA, was passed nearly unanimously by each chamber of Congress.

Under a Democratic-controlled House, that unity is unlikely to change. Representative Eliot Engel, an outspoken critic of the Kremlin and defender of Russia's beleaguered human rights community, is likely to take chairmanship of the House Foreign Affairs Committee.

Another Russia critic, Adam Smith, is likely to take over as head of the House Armed Service Committee.

Prior to the election, the Senate was already losing a key figure in the effort-- pushed by Republicans and Democrats alike -- to keep pressure on Moscow. Bob Corker, chairman of the Senate Foreign Relations Committee, decided to retire rather than face a challenge in the primary election.

As the senior Republican on that committee, Jim Risch is widely expected to succeed Corker. He is not considered to be as hawkish on Russia policy as Corker, or as the other Republican who has expressed interest in the chairmanship -- Marco Rubio. Risch is not known for challenging the White House, whereas Rubio ran against Trump in 2016, and may run again in 2020.

The Senate also lost one of its most authoritative voices on Russia -- John McCain, who died in August. As the chairman of the chamber's Armed Services Committee, he also helped steer U.S. defense policy, including in Europe, where Washington has conducted a slow buildup of forces and equipment in response to Russian actions in Ukraine and elsewhere.

Chairmanship of that committee was taken over by James Inhofe following McCain's death, and he's expected to remain in that position. Inhofe has voted alongside his Republican colleagues in favor of CAASTA, but is not nearly as outspoken as was McCain.

Some Senate Democrats, including Robert Menendez, who barely won reelection, have pushed to ratchet up pressure on Russia by, among other things, making it harder for Russia to issue sovereign debt.

Little change, if any, is expected in the congressional approach toward Ukraine, which has had mostly solid backing from both Republicans and Democrats over the past two years. House Democrats may consider funding for more weapons supplies to Ukraine's armed forces.

​IRAN

The U.S. approach to Iran took a sharp tack to the right not long after Trump took office. Many Republican lawmakers, as well as many of Trump's top advisers, were deeply skeptical of President Barack Obama's approach toward Tehran, which including the landmark 2015 nuclear deal.

Many Democrats were supportive of the deal, under which world powers lifted crippling economic sanctions in exchange for Iran curbing its nuclear ambitions.

Trump has since reimposed the U.S. measures dropped under the 2015 deal, and further targeted Iran's ballistic-missile program and involvement in the Middle East with what his administration has called the "toughest-ever" U.S. sanctions against Tehran for its actions in the Middle East.

Even with the Democrats in control in the House, given that the authority to impose economic and other sanctions falls primarily to the White House, Trump is expected to continue tightening the screws on Iran.

Still, as with other matters, House Democrats will be able to call in Trump advisers to testify and explain the administration's reasoning -- potentially under oath -- regarding Iran-related policy.

In Congress, Iran was included in the CAATSA legislation, and leading Republican senators such as Tom Cotton of Arkansas have endorsed the hard-line approach, and pushed for even more punitive measures.

Still other Republican senators, such as Rand Paul of Kentucky and Mike Lee of Utah, have been adamantly against any financing for any war effort that Trump's most anti-Iranian advisers may be pushing.

​The White House And The House Of Saud

Saudi Arabia is Washington's closest Muslim ally in the Middle East, buying billions of U.S. armaments, keeping world oil markets stable, and playing an often behind-the-scenes role in the Middle East's conflicts.

But relations with the United States have been severely strained following the killing of Jamal Khashoggi, a Saudi journalist who was a critic of Saudi Crown Prince Mohammed bin Salman.

Kashoggi, who also had legal residency in the United States, was allegedly killed by a special team of Saudi agents after entering the Saudi Consulate in Istanbul on October 2. Trump is facing bipartisan pressure to take action against Riyadh. Last month, 20 senators, Democrat and Republican, signed a letter to the White House suggesting that sanctions be imposed on Saudi officials linked to Kashoggi's killing under human rights legislation known as the Global Magnitsky Act.

As with other foreign-policy areas under Trump, relations with the Saudi kingdom under Trump have been managed largely through the White House; Trump's son-in-law Jared Kushner has had the portfolio over managing a large part of U.S. policy in the Middle East, and he cultivated close ties with Saudi leaders.

On the House side, expect Democrats to not only push the White House on the Kashoggi killing, but also pry deep into Kushner's dealings with the Saudi leadership and business leaders.

Meanwhile, the civil war in neighboring Yemen -- where U.S. supplied jets are used by the Saudi air force in attacking Iranian-backed Huthi rebels -- is increasingly becoming a humanitarian disaster. A growing number of lawmakers have spoken about reining in Saudi-led operations, including Engel, the likely next chairman of the House Foreign Affairs Committee.

A Democratic-led House could do myriad things to punish Riyadh, including voting to block arms deals or stymie any effort by the Saudis to reach a nuclear energy deal with the United States --something that has reportedly been discussed in the administration.

Still, in a further indication that the administration's attitude to the Yemen war may have already started shifting, Secretary of State Mike Pompeo and Secretary of Defense Jim Mattis on October 31 called for a participants in the Yemen war to agree to a cease-fire.

THE MUELLER FACTOR

Special Counsel Robert Mueller's investigation into Russia's interference in the 2016 presidential election -- as well as interactions between Trump associates and Russian officials-- is the darkest shadow hanging over the Trump administration.

Mueller took over an existing FBI investigation that was started four months before the November 2016 election, and his continuing efforts have infuriated Trump.

To date, Mueller's team has netted seven guilty pleas or convictions and brought indictments against 26 more individuals, and three Russian companies.

House Republicans have shown little inclination to buttress Mueller's probes. Some Republicans have asserted that Mueller's team is biased against Trump, because, for example, some may have made campaign donations to Democratic political candidates in the past.

Under the leadership of Mike Conaway, House Republicans ended the Intelligence Committee in March, concluding there was "no collusion" between Trump's election campaign and Russian officials. Democrats on the panel largely boycotted the findings.

That will change immediately under House Democratic leadership.

Representative Adam Schiff is expected to take over leadership of the Intelligence Committee, and with many House Democrats -- not to mention Democratic voters -- pushing hard for aggressive digging, he'll be under pressure to start subpoenaing witnesses and documents.

On the Senate side, the Intelligence Committee has worked more diligently, as the Republican chairman, Richard Burr, and the ranking Democrat, Mark Warner, have forged a collegial relationship. Warner is expected to assume control of the panel; Burr's presence may or may not continue.

Regardless, the first test of the willingness of House Democrats, and Senate Republicans, to push back against Trump is expected to come within weeks. Trump has signaled he plans to fire, or push out, Attorney General Jeff Sessions, who angered Trump when he recused himself from oversight of Mueller probe.

If Sessions is forced out, the fate of his deputy, Rod Rosenstein, who does have authority over Mueller's probe, will also become an open question.

And if Trump moves to fire or otherwise pressure Mueller, House Democrats can be expected to initiate impeachment proceedings.