Before the afternoon hearing, Menendez made the rounds of major TV networks, and, along with other senators, met with Obama at the White House. At each stop, he forcefully pushed for limited military action, despite widespread public opposition to such steps.
"The images of that day were sickening," Menendez said at the hearing, referring to the Aug. 21 chemical-weapons attack on a Damascus suburb that the administration says killed more than 1,400 people. "In my view, the world cannot ignore the inhumanity and the horror of this act."
Menendez noted that he has backed military action in Syria despite voting against the second Iraq war.
Sen. Bob Casey (D., Pa.), who has closely watched Syria, has been another early advocate for military action.
Menendez and Sen. Bob Corker of Tennessee, the committee's top Republican, released a draft resolution late Tuesday that would allow use of military force in Syria for up to 60 days - with the possibility a 30-day extension - but would bar use of ground forces in combat. A committee vote was planned for Wednesday.
Leading a hearing that brought an early end to Congress' summer break, Menendez argued that striking Syria was in the U.S. national interest. Failing to do so, he said, would embolden adversaries such as Iran, North Korea, and al-Qaeda.
"A precedent will be set either for the unfettered and unpunished use of chemical weapons, or a precedent will be set for the deterrence of the use of such weapons," he said. He later added, "Clearly, at the end of the day, our national security is at stake."
One of Menendez's opening questions prompted a dramatic moment in the hearings, causing Kerry to stumble into a suggestion that the administration would not want to entirely rule out the possibility of putting "boots on the ground" in Syria.
Kerry, who was Menendez's predecessor as Foreign Relations chairman, backtracked later in the hearing.
For Menendez, the debate on Syria represents the most volatile issue he has had to confront in his short tenure as chairman. In January he led a much-watched hearing on the attacks on the U.S. Consulate in Benghazi, Libya - but that was after the incident, and there was little debate about future actions.
While Menendez has sometimes bucked Obama on foreign policy - pushing for stronger Iran sanctions than the administration preferred, for example - he has been an ally on this issue.
The two hearings have been part of a roller-coaster 10 months since Menendez won reelection in November. He led the Benghazi hearing and became committee chairman, was embroiled in an ethics controversy involving a major campaign donor, and then was a central figure in the Senate's approval of an immigration overhaul.
Now, he finds himself as a key player in a global issue.
The debate is also familiar to Casey, who until July chaired a subcommittee that oversees the region that includes Syria.
In supporting a military strike, Casey spoke of the message that would be sent to North Korea and extremist groups such as Hezbollah if the United States doesn't act.
"We don't want to send a message of weakness . . . nor do we want to send a message that we don't mean what we say," he said. "This message is much bigger than Syria."
Local Republican senators are among the many lawmakers wary of authorizing an attack.
Sen. Pat Toomey (R., Pa.) is undecided, according to an aide, and Sen. Jeff Chiesa (R., N.J.) "is reviewing" Obama's request, a spokesman said.
Both are seeking additional information in briefings.
Many fear being drawn into a Syrian civil war that few Americans have an appetite for. Not even supporters of a military strike believe missiles will significantly change the course of the internal conflict.
"I'm a bit skeptical . . . that what the president is asking for will provide the support needed to achieve these objectives," Rubio, of Florida, said at the hearing, referring to the idea of holding the Syrian regime accountable and damaging its ability to use chemical weapons.
"I can't send anybody to war when our goal is stalemate," Paul, of Kentucky, said on CNN after the hearing. "I can't see anyone's son or daughter fighting for that."
Casey, though, predicted that, as lawmakers learn more from the administration this week, they will authorize a military strike.
Contact Jonathan Tamari at email@example.com or follow on Twitter @JonathanTamari. Read his blog, "Capitol Inq," at www.inquirer.com/CapitolInq.