Three years after President Obama’s infamous “red line” threat to Syrian President Bashar al-Assad, charges of chemical weapons use inside the war-torn country persist -- in turn fueling concerns about whether Iran can be held to the newly struck nuclear deal. 

Assad reportedly is developing a new type of chlorine bomb, and earlier this year investigators found trace components of sarin and VX, an extremely toxic manmade chemical nerve agent. This, despite a 2013 deal between the U.S. and Syria to purge Assad's chemical weapon stockpile -- a deal meant to de-escalate the standoff with the West after allegations he crossed Obama's "red line" with chemical weapons. 

As the anniversary of that warning hit, Obama's foreign policy critics were quick to remind him of Assad's defiance. "Three years ago today ... President Obama made his infamous 'red line' comment. Assad subsequently ignored the president's hollow warning," GOP presidential candidate and Wisconsin Gov. Scott Walker said in a statement Thursday. "President Obama's meek response to this atrocity sent a devastatingly clear message of weakness to our enemies: you will not pay a price for defying our commander-in-chief." 

While Assad's activities largely have been overshadowed by the Islamic State's atrocities, the unresolved chemical weapons issue still hangs over the Iran nuclear debate today. Critics of the deal argue that if the administration is unable to enforce its highly touted chemical weapons pact with Syria’s leader, promises made about the strength of the nuclear deal with Iran should raise red flags.  

“I think the failure of the Obama administration’s agreement on Syria’s chemical weapons disarmament should be a powerful wake-up call about the prospects for success of its flawed nuclear agreement with Iran,” Jim Phillips, senior research fellow for Middle Eastern Affairs with the conservative Heritage Foundation, told FoxNews.com.

At the least, leaders in both Syria and Iran have proved defiant in the wake of these agreements. 

On Monday, Iran's Supreme Leader Ayatollah Ali Khamenei said the country will remain closed to U.S. influence and continue to oppose American policies regardless of whether a deal is signed.

“They thought this deal – and it is not clear if it will be passed in Iran or in America – will open up Iran to their influence,” Reuters reported Khamenei saying at a meeting with members of the Islamic Radio and Television Union. “We blocked the path and will definitely block it in the future. We won’t allow American political, economic or cultural influence in Iran.”

Apprehension of the Iran deal grew greater Wednesday following an Associated Press report on a secret agreement between Iran and the International Atomic Energy Agency allowing Iran to use its own experts to inspect a site it allegedly used to develop nuclear arms. While the IAEA and State Department disputed the report, the news drew immediate ire from critics who have cautioned the deal's success relies too heavily on taking Iran at its word – as with Syria – to do the right thing.

Earlier this year, Sen. Tom Cotton, R-Ark., also warned Iran would look at America’s response to allegations Syria was still using chemical weapons as proof there would be few – if any – consequences to breaking a deal.  

“Anyone with eyes to see knew the message President Obama had sent,” Cotton said from the Senate floor in May. “When he flinched in 2013 in the face of Assad’s regime brutal and brazen use of sarin gas against civilians, it only emboldened Assad to test U.S. resolve.”

Phillips told FoxNews.com he sees troubling similarities in how the Obama administration has handled the two allied countries. “In both cases, the administration underestimated the willingness and capacity of a hostile dictatorship to violate an arms control agreement after international pressure was defused by the signing of the agreement,” he said.

The 2013 agreement with Syria, which was heralded by the Obama administration as a foreign policy win, required the country to destroy its chemical weapons. But many Middle East experts believe Syria is following the same predictably deceptive game plan used by North Korea and Libya in the past. 

The Syrian American Medical Society, a U.S.-based charity that operates more than 90 makeshift medical facilities on Syria’s frontlines, says they’ve compiled a list of detailed attacks -- including chemical -- that have taken place since the 2013 pact. In its latest 2014-2015 report, SAMS President Dr. Mohammed Zaher Sahloul, says he’s “run out of words to describe the collective suffering of Syria’s children.”

Since 2011, there have been more than 615 health workers killed in Syria.

In September 2014, the Organization for the Prohibition of Chemical Weapons ruled with “a high degree of confidence” that chlorine was used repeatedly in attacks in northern Syria. 

In contrast to stronger nerve agents, chlorine typically kills only in highly concentrated doses. In low doses, it’s commonly used as a disinfectant agent and wasn’t on the list of chemicals Assad promised to get rid of.

In March, members of the U.N. Security Council, many who cried after seeing footage of three young children choking to death allegedly from a chlorine gas attack in Sarmeen, a village in northwestern Syria, condemned the chlorine barrel bombs but did little else. The attacks were first reported by the Syrian Observatory for Human Rights. The group claimed six people -- three children and three adults – had been killed in the attack. The group said dozens of the others had been wounded.

Secretary of State John Kerry condemned the attacks and said the U.S. was “deeply disturbed” by the allegations, calling for a quick investigation into the matter. The U.N. since has empowered a team to investigate allegations and determine blame. 

Human Rights Watch also had urged the U.N. Security Council and others to "respond strongly" to evidence of "chemical warfare." In May, diplomats said they found traces of sarin and VX, renewing concerns Syria did not disclose the entirety of its weapons program. The Wall Street Journal in June reported that U.S. officials suspect Syria might still have a reserve of the chemicals needed for sarin or VX.

The White House last updated its Syria chemical weapons attacks page on Oct. 31, 2014. 

“The U.S. State Department has been looking into reports of chlorine gas attacks since at least April 2014,” Phillips, a Syria scholar, said. “The administration is slow-walking its investigation.”