President Trump hasn't implemented a military plan to prevent Russia and Iran from dominating Syria and threatening the west, a top Republican lawmaker warned.

"They picked the best small footprint option that they could for the maximum amount of impact," House Intelligence Committee chairman Devin Nunes, R-Calif., told the Washington Examiner. "Meaning: small troop numbers; heavy involvement with our partners; but in the long run, I don't know if that's going to be successful."

That's a sharp warning from a top Republican lawmaker, one who defended Trump in the midst of a political storm over the president's claim that former President Barack Obama's team "wiretapped" his campaign. It reflects growing concern that the United States is risking defeating the Islamic State in Syria only to see that territory dominated by another major source of terrorism: Iran, which has partnered with Russia in propping up Syrian President Bashar Assad.

"I believe that we'll continue to take out ISIS leadership and create havoc for ISIS and al Qaeda in the region; however, you take the longer term risk of empowering the [Iran-backed] Shias and the Russians and the Assad regime to create more havoc for the West," Nunes said.

While ISIS has dominated international headlines, all the major players in the Syrian civil war have recognized longer-term stakes to the fight. An American-led coalition has focused on recapturing Raqqa, the chief stronghold of ISIS. Russia and Iran have prioritized propping up Assad, sometimes by attacking U.S.-backed forces. That tension culminated in the downing of a Syrian warplane by a U.S. fighter jet on Sunday, which outraged the Russians.

"Any aircraft, including planes and drones of the [U.S.-led] international coalition, detected in the operation areas west of the Euphrates River by the Russian air forces will be followed by Russian ground-based air defense and air defense aircraft as air targets," the Russian Defense Ministry said in response.

That's a far cry from Trump's goal, often stated during the 2016 campaign, of working with Russia to fight terrorism. Russian President Vladimir Putin regards the threat of ISIS as secondary to keeping the Assad regime in power, in part because Assad has given the Russian military the use of a port on the Mediterranean Sea.

Putin's partner in the country, Iran, is fighting to take control of territory formerly held by ISIS that will allow the Iranian regime to have direct contact with Lebanon, which borders Israel and is the home of their main terrorist ally, Hezbollah.

"One of my highest concerns is the Iranians' ability to get a land bridge out to the Mediterranean to increase their logistical support for terrorist networks," Nunes told the Washington Examiner. "You've got the largest state sponsor of terrorism, Iran -- if they get the logistical capability to move massive amounts of weapons and equipment and God knows what else quickly to the west, it's a real danger."

If Russia and Iran achieve their objectives after the U.S.-coalition orchestrates the defeat of ISIS, that will leave both adversaries in a stronger position to pressure the West, according to U.S. lawmakers in both parties.

"The day after Raqqa falls is going to be the moment that Iran moves to try to oust the United States from the region," Sen. Marco Rubio, R-Fla., told the Washington Examiner in February.

New York Rep. Eliot Engel, the top Democrat on the House Foreign Affairs Committee, concurred.

"I do think there will be some collusion between Russia and Iran," he said. "I worry about it."