Lawmakers say Annan's departure is sign of worse to come for Syria

“The increasing militarization on the ground,” Annan said, “and the clear lack of unity in the Security Council have fundamentally changed the circumstances for the effective exercise of my role.”

Annan was named to the role in February. More than 17,000 people have died since the revolt against Assad's rule began a year and a half ago. 

The Obama administration said it wasn't surprised by Annan's decision.

“I think we’re not surprised that the Joint Special Envoy was at a point where, given the regime’s intransigence, he thought it was the appropriate time to step down,” said State Department spokesman Patrick Ventrell.

Lawmakers agreed.

"I think it's further evidence of the very serious and detrimental situation in Syria," said House Foreign Affairs Committee member David Cicilline (D-R.I.), adding that Annan's decision showed "growing frustration over the value of his continued role."

“I think the fact that he's stepping down shows that things were remote to start with,” said Sherman. “It's a sign of his frustration and the world's frustration. Our frustration is with the governments of Iran and Russia that have provided different levels of support for Assad, and at the same time we shouldn't fool ourselves into thinking that the resistance to Assad is all inspired by Jefferson and Franklin.”

Other lawmakers, however, said the announcement opens the door for further U.S. intervention.

“He's done two things there,” said House Armed Services Committee member Trent FranksHarold (Trent) Trent FranksReal-time data insights have become a powerful political tool Tillerson announces mandatory sexual harassment training for State Dept. Dems blast RNC over Steve Wynn sexual misconduct claims: 'This is the party of Donald Trump' MORE (R-Ariz.). “He's made a statement that will only increase the pressure on the Syrian government, and possibly open the way for more direct influence either by indirect support or soft support on the part of the United States for the insurgents.”

Franks cautioned however against arming the rebels without knowing who they are.

'The challenge is you have some people fighting him who genuinely are seeking freedom and you have some groups there who are trying to exploit that and gain power themselves and maybe take Syria from the frying pan into the fire,” Franks told The Hill. “That's the challenge. That's why I say that direct military intervention right now is, I think, premature until we know who is going to be replacing [Assad]. Our influence needs to be applied toward making sure that any replacement in Syria is a genuine democratically chosen government that is not of the al Qaeda or Muslim Brotherhood genesis.”

Rep. Ed Royce (R-Calif.), the chairman of the Foreign Affairs Committee's nonproliferation panel, said Annan's departure was further proof of Russia's misguided support for a government that could lose control of its chemical weapons stockpile if the violence continues.

“They should be most concerned about how you wind this thing down peacefully,” Royce said. “If they were to be clear-eyed about this, they'd realize that to get these weapons into the trading bazaars along the Silk Road is ultimately to threaten the under-belly of Russia itself. That I think is our real frustration about Russia being part of the problem rather than part of the solution.”