(NewsNation) — Secretary of State Antony Blinken on Thursday said the U.S. has “put forward a serious proposal” for Paul Whelan’s release and that “Russia should take it.” Whelan’s brother, David, told NewsNation he is “cautiously optimistic” about Blinken’s statement.

Blinken’s comments came after he briefly met with Russian Foreign Minister Sergey Lavrov. With another 12 years left on Paul’s sentence, David says he doesn’t get his hopes up very high with remarks.

“We will be cautiously optimistic. I think at the end of the day, we’re waiting for the thugs and the thieves in the Kremlin to decide that it’s time to let Paul go and that they will take something for him,” David told NewsNation Prime’s Natasha Zouves. “So until that happens, I think we just have to continue to wait.”

Whelan, 53, is a former U.S. Marine who was arrested at a Moscow hotel in 2018. Russia insists that Whelan, a Michigan corporate security executive, is a spy. Whelan has denied their claims, his family saying he was in Russia for a wedding.

Whelan received a 16-year prison sentence in Russia on espionage charges that the U.S. has called politically motivated.

Details of the U.S. proposal for the potential release of Paul were not immediately released to the public or to the Whelan family.

“We don’t really know what the State Department is up to. We do know that they have been trying a number of different tactics to get the Kremlin to release Paul. And so I don’t know if this is similar to the proposal that was made last summer that Secretary Blinken talked about last year, or if this is a new one, but they are trying everything as far as we can tell, to bring Paul home,” David said.

The ”proposal” comes as the U.S. is at what may be seen as low U.S.-Russia relations. After Russia’s invasion of Ukraine, Congress has approved more than $130 billion in aid to Ukraine, according to reports.

“Obviously the people in the Kremlin aren’t making great decisions right now, and I think not releasing Paul is another bad decision,” David added.

David said he’s not sure what exactly it would take to convince Putin to release Paul, but he has a hunch it’s about what will best serve Putin.

“I think it’s definitely about what President Putin sees in his self-interest and the self-interest of his government, the ability for him to survive as a political leader and also just as a human,” David said. “I think eventually he will find something that will persuade him to release Paul, but I’m not sure what it would be.”

The prisoner swaps of Marine veteran Trevor Reed and all-star basketball player Brittney Griner raised both hopes and concerns for Paul’s case.

When Reed was released, some wondered if the U.S. would make a prisoner exchange for the freedom of both Griner and Whelan. After the exchange of solely Griner for Viktor Bout, a notorious arms dealer known as the “Merchant of Death,” some questioned whether the White House lost leverage and made a bad deal that did not include Whelan.

In a spot of political vulnerability following Griner’s release in December, President Joe Biden insisted his administration had “not forgotten about Paul Whelan.” Biden said Russia for “totally illegitimate reasons” placed Whelan’s case in a different light than Griner’s.

“While we have not yet succeeded in Paul’s release, we are not giving up,” Biden said in December. “We will never give up.”

Months later, Paul is celebrating his birthday in a Russian prison camp.

“It’s his birthday,” David said Sunday. “He was able to have a potluck with some other prisoners in the camp, so they were able to share food and have as good a day you can in 20-degree Mordovian weather.”

David continued: “He’s doing a great job of surviving and we hope that he will survive for as long as it takes for him to get home.”

Biden has previously said his administration is going to keep working to bring every American enduring such injustices home.

According to the James W. Foley Legacy Foundation, there are currently 60 Americans, including Paul, being wrongfully detained or held hostage.