Before President Obama forced his Iran nuclear deal into effect despite majority congressional opposition, lawmakers fretted about how Iran might spend the $1.7 billion windfall headed its way.

It was one of their main objections to the deal. Iran is the world's leading state sponsor of terrorism, and for 37 years has funded paramilitary activity designed to destabilize and weaken its regional neighbors, including Iraq, Israel, the Palestinian territories, Lebanon and now Yemen.

Obama insisted on separating sanctions surrounding Iran's nuclear program from discussion of Iran's international terrorism, even though the lifting of the former could obviously finance the latter. Now a group of senators is pointing to evidence that it has, and is asking the Obama administration uncomfortable questions.

When the public reads about Syrian forces using chemical weapons, murdering children and bombing United Nations relief convoys, it should think of Obama's Iran deal because the two are connected.

Syria's government depends on Iran and the militias it funds because it cannot win the civil war on its own. This is why the siege of Aleppo has dragged on for four years, putting the civilian population through unending hell. Bashar Assad, the country's tyrant, is incapable of crushing opposition groups, a small number of which are weakly propped up by feeble American efforts.

Iran, as the senators pointed out this month, is using sanctions relief from Obama's nuclear deal to provide Assad with additional help. We're referring here not just the pallets of cash Obama sent to the mullahs. There is also a deal to sell aircraft to an Iranian airline known for smuggling weapons.

Obama approved, again over the objection of Congress, a deal that allows Airbus and Boeing to sell nearly 200 airplanes to Iran Air, a carrier sanctioned since 2011 for shipping weapons for terrorists, and for breaking international law by concealing them on supposedly civilian flights.

Iran Air, the senators say, "continues to fly from known [Iranian Revolutionary Guard] bases in Iran to Syria." Those planes are probably not carrying tourists.

Given that Iran Air lacks the capacity to operate such a large fleet, it is likely that many of the planes that are to be sold will be loaned to other Iranian airlines — they specifically mention Mahan Air — that are still under sanctions. The senators wisely question whether the administration has made contingency plans for what happens if the airliner deal falls through on account of Iran Air's illegal activities, or of the use of purchased planes for illegal activity by third parties.

To date, Iran has taken skillful advantage of every unwise concession from Obama and Secretary of State John Kerry in the negotiation of the nuclear deal. This is one more area where the deal is proving worse even than the one Obama promised and which still failed to convince Congress. There is a reason why top Clinton aide John Podesta, when presented in a private email with Sen. Mark Kirk's statement that "This is the greatest appeasement since Chamberlain gave Czechoslovakia to Hitler," merely replied, "Yup."

As the various presidential candidates struggle to describe anything they can do to improve the situation in Aleppo, they would do well to address what the Obama administration is doing right now to make it worse.