A pair of Trump associates, Michael Cohen and Felix Sater, appear to be gaining significance in the Trump-Russia investigation. News broke this week that during the presidential campaign the two sought a deal for the construction of a Trump Tower in Moscow. And, as reported earlier this year, the pair pushed a Kremlin-backed proposal for the US to lift sanctions on Russia—part of a proposed “peace deal” between Ukraine and Russia that Cohen and Sater brought to Trump’s then national security advisor Michael Flynn.

Congressional investigators are now interested in how the Moscow tower proposal and the so-called peace deal may connect. “That is a question members will be exploring, certainly,” says an official close to the Senate Intelligence Committee. One thread running through both deals is Russia’s desire for relief from US sanctions, which the Trump presidential campaign repeatedly signaled it was interested in accommodating. How that might shed further light on the deals is a “very interesting line of inquiry,” the official adds.

Cohen claims that he pulled the plug on the Moscow tower deal in late 2015. But after Trump took office, Cohen and Sater went on to push a “peace plan” under which the US would unwind economic sanctions in exchange for the withdrawal of pro-Russian troops from Ukraine and an agreement to hold a referendum on the fate of Crimea, the Ukrainian territory Russia seized in 2014. Cohen hand-delivered the proposal to Flynn, who was soon forced to resign over matters including his lying about having discussed sanctions with the Russian ambassador to the US.

The peace plan came from Andriy Artemenko, a Ukrainian lawmaker known for his pro-Kremlin views, who told the Times that senior aides to Putin encouraged him to push the plan. Artemenko said he contacted Sater through an unnamed “mutual friend,” who worked with Cohen to get the plan to Flynn. It is not clear if Trump himself reviewed the plan, though around the same time the president reportedly asked the State Department to look into the possibility of unilaterally rescinding sanctions on Russia.