Moqtada al-Sadr, the firebrand Shiite cleric, maintains close ties to Tehran. (Associated Press)

The planned withdrawal of all American troops from Iraq has raised tough questions about that country’s ability to manage its security challenges. It is also reviving familiar concerns about another country: Iran.

Since President Obama’s announcement of the withdrawal Friday, his top aides have been pressed repeatedly on the the threat posed by Iran as the Americans pull out. The fear, of course, is that the country’s Shiite leadership could attempt to exercise its influence in Iraq, inciting strife with Iraqi Sunnis and injecting a combustible element into a country still beset by sectarian divisions.

American officials are now going out of their way to emphasize U.S. capacity in the region, suggesting that that alone should serve as a bulwark against Iran.

By Defense Secretary Leon Panetta’s count, that’s 23,000 American troops in Kuwait, 7,500 in Qatar, 5,000 in Bahrain and nearly 3,000 in the United Arab Emirates.

“We have about 40,000 troops in that region ... along with a large number of troops in other countries as well, along with the fact that we have 100,000 troops in Afghanistan,” Panetta said Sunday during a trip to Bali. “We will always have a force that will be present and that will deal with any threats from Iran.”

Secretary of State Hillary Rodham Clinton, asked on CNN’s State of the Union about her fears that Iran might try to increase its presence in Iraq, said “we have bases in neighboring countries, we have our NATO ally in Turkey, we have a lot of presence in that region.”

“So no one, most particularly Iran, should miscalculate about our continuing commitment to and with the Iraqis going forward,” she said.

Even with the departure of the remaining 39,000 U.S. troops in Iraq, there will still be opportunities for limited training by the Americans.

Panetta has pointed to the 150-person military unit in the U.S. Embassy’s Office of Security Cooperation, which along with a large number of contractors, will provide training on newly purchased American F-16 fighter-bombers and M1A1 Abrams tanks. Denis McDonough, White House deputy national security adviser, told PBS’s News Hour on Friday night that the United States and Iraq would still conduct periodic naval and air exercises.

But whether those kinds of limited military ties – and the U.S. footprint in the region — will be enough to prevent Iran from trying to expand its activities in neighboring Iraq, and inciting sectarian strife, is far from clear.

Moqtada al-Sadr, the Iranian-back Shiite cleric and anti-American firebrand, has made clear that any attempt by the Americans to extend their military ties to Iraq would be fiercely resisted.