CNBC
The president of the United States has very different attitudes toward the two biggest supporters of one of America's greatest enemies.
Both Iran and Russia support Syrian strongman Bashar Assad, who has committed atrocities against his own people in that country's bloody civil war. Trump has been candid about his distrust of Tehran, but he has been less critical — sometimes even supportive — of Moscow.
Trump is a recurring and vocal critic of Iran. He opposes a nuclear deal struck in 2015 between Iran and a group of major powers including the Obama administration, calling it the "worst deal ever" and vowing to "rip it up."
In a May speech in Saudi Arabia, Trump condemned Iran for supporting militias, terrorists and other extremist groups.
"Among Iran's most tragic and destabilizing interventions have been in Syria. Bolstered by Iran, Assad has committed unspeakable crimes," he said.
With Russia, Trump has taken a more positive tone. He has tweeted that having a good relationship with Russia is a good thing, and that only "stupid people" would disagree.
The U.S. has been slow to realize Russia's "power projection issues" in the Middle East, said Andrew Bishop, deputy director of research at the Eurasia Group, whereas Iran ambitions in the region are longstanding and well-known. Plus, Bishop said, Trump may perceive Russia as a fellow target of Islamic terrorism and one of few potential partners in Syria.
The president has voiced his desire to work with Russia to fight the Islamic State group, also known as ISIS.
The U.S. Senate appears ready to ensure that the administration doesn't unilaterally ease up on Russia. On Wednesday, the Senate voted overwhelmingly to require the president to get congressional approval before he lifts any sanctions against the country.
Three approaches toward Assad and ISIS
The U.S., Russia and Iran are all deeply involved in Syria, though in radically different ways.
Russia supports the Assad regime through financial aid, trade agreements, heavy weapons, air support, military guidance and diplomatic assistance, said Faysal Itani, resident senior fellow at the Atlantic Council's Rafik Hariri Center for the Middle East.
Iran helps the regime by deploying its own militias in the country and supporting groups such as Hezbollah that are fighting on the ground for Assad. Iran also assists with military training and financial support.
"Think of Iran as the ground force responsible for Assad's survival," Itani said. "I think both are essential to the war effort, but that Iran is the party more deeply invested and with far more influence on the ground, including over Assad."
The U.S. began arming moderate Syrian rebels in 2013, two years after the Syrian civil war started. It avoided direct confrontation Assad until this year, when the regime reportedly used chemical weapons on its own people in April. The Trump administration directed a missile strike on an air base in Syria — prompting condemnation from both Syria and Russia.
Regardless of their differing attitudes toward Assad, the U.S., Russia and Iran share one enemy: ISIS. Defeating the bloodthirsty group is one of the few goals the U.S. and Iran share anywhere, Bishop said. Iran has helped push back ISIS, particularly in Iraq, but its successes come with the risk of growing Iran's influence in the region.
"This goes at the heart of one of the key tensions within U.S. policy, especially within the Trump administration's policies, which is that the Trump administration would like to ideally push back against ISIS and Iran simultaneously," Bishop said. "But they quickly realized they may have to prioritize one against the other."
In the end, working with Russia could benefit the U.S. in a complex situation, Itani said.
"We don't have a choice but to oppose Iran and try to accommodate Russia," Itani said. "It's the only conceivable way of bringing an end to the war on terms the United States can accept, i.e., without turning over the entire country to Iran. If we are indeed able to divide Russia from Iran, we stand a much better chance of forcing an outcome in Syria that serves our interests."