By Tom Curry, National Affairs Writer, NBC News

White House Chief of Staff Denis McDonough said Sunday that an impending U.S. attack on Syria would send a message to Iranian leaders that they should not feel free to develop nuclear weapons.

McDonough said on NBC’s Meet the Press that “to communicate with them we have to be very clear, very forthright. This is an opportunity to be both with the Iranians....”

He said, “nobody is rebutting the intelligence; nobody doubts the intelligence” that is the basis for President Barack Obama pinning the blame for an August 21 chemical weapons attack in Syria on President Bashar Assad's regime which is fighting to suppress a rebellion that began in 2011.

White House Chief of Staff Denis McDonough visits Meet the Press to discuss recently released footage of a chemical assault on the Syrian people.

McDonough noted that “our troops have not been subject to chemical weapons attacks since World War I” and argued that “we have to make sure that for the sake of our guys – our men and women on the front lines – that we reinforce this prohibition against using chemical weapons.”

If Assad is not deterred, he will put chemical weapons on the front lines in his battle against the Syrian rebels and that would mean “a greater risk of them being proliferated” and perhaps falling into terrorists’ hands, McDonough argued.

He added that “the momentum on the battle field will be changed by a targeted, limited effort” but he said ultimately “there’s not a military resolution” to the civil war in Syria, only a “political, diplomatic resolution.”

McDonough’s appearance on Meet the Press and other Sunday talk shows was one part of an intense public offensive headed by Obama himself, including the president doing interviews Monday with six television networks and culminating in his speech to the nation Tuesday night.

McDonough said Obama wants Congress to be “a full partner” in military action against Assad’s regime.

Obama faces one of the crucial weeks of his presidency with the Senate headed for a vote as early as Wednesday to end debate on a measure authorizing an attack on Syria; the measure’s supporters need 60 votes to move it ahead to final passage.

Reaction from members of Congress has ranged from endorsing an attack to wariness to fervent opposition.

The division on the issue hasn’t followed party lines.

Sen. Tom Udall, D- N.M., who voted against the resolution authorizing use of military force last week in the Senate Foreign Relations Committee, said on Meet the Press Sunday that he was “very disappointed that the administration has given up” on the United Nations and “on rallying the world.”

The American people, Udall said, “don’t want to be embroiled in a Middle Eastern civil war; this is an act of war that we’re going to take. We haven’t exhausted all of our political, economic, and diplomatic alternatives.” Obama, he charged, “is moving much too rapidly down the war path and not trying to find a political solution….”

Another Democrat, Rep. Loretta Sanchez, D- Calif. said she was leaning against the resolution authorizing use of force. She said it is not clear to her that United States national security is directly at risk from Assad’s regime. “I haven’t heard that Assad wants to use the weapons against us; I haven’t heard that he wants to use the weapons against our allies (or ) that he’s moving them to terrorist organizations.”

She said, “The minute that one of those cruise missiles lands in there, we are in the Syrian war. It’s a civil war and we’re taking sides with the rebels,” some of whom, she said, were linked to al Qaeda.

Sanchez indicated that she’s quite skeptical of Obama’s argument that any military action will be carefully limited: “For the president to say, ‘this is just, you know, a very quick thing and we’re out of there.’ That’s how long wars start.”

Republican Rep. Mike McCaul of Texas, chairman of the House Homeland Security Committee, who he said he couldn’t support Obama’s plan, agreed with Sanchez: “Once we hit, this is an act of war. Little wars start big wars.” He called an attack on Assad “kind of a face-saving measure” by Obama “after he drew the red line” against use of chemical weapons by Assad’s regime.

Even Rep. Peter King, R- N.Y., who supports an attack on the Assad regime and warned Sunday of the danger of an “Iran-Syrian axis in the Middle East,” harshly criticized Obama whom he said has been “vacillating. I can’t imagine Harry Truman or John Kennedy or Ronald Reagan or Dwight Eisenhower ever putting the nation in a position like this….”

He said, “I wish he was more of a commander-in-chief than a community organizer.”

In another example of the Syria issue crossing party lines, Sen. Mark Pryor, D- Ark, who is up for re-election next year, announced Saturday that he opposes an attack, while his Republican opponent, Rep. Tom Cotton, has said he strongly supports military action and wants to go even further and topple the Assad regime to achieve “an ultimate victory in Syria” with “a pro-Western, moderate native Syrian government” taking Assad’s place.

Pryor said Saturday that the Obama administration had to “prove a compelling national security interest, clearly define a mission that has a definitive end-state, and then build a true coalition of allies” that would take part in action against Assad. But “based on the information presented to me and the evidence I have gathered, I do not believe these criteria have been met, and I cannot support military action against Syria at this time,” Pryor said.

Obama said Friday, “it’s conceivable that at the end of the day I don’t persuade a majority of the American people that it's the right thing to do,” but he added that sometimes members of Congress must do what they think is right even if they go against their constituents’ wishes.

Obama has not explicitly said whether he might choose to launch an attack anyway even if Congress votes down a resolution authorizing him to attack Syria. He rebuffed reporters’ questions on that point in a press conference Friday at the meeting of G-20 nations in St. Petersburg, Russia.

Meanwhile, Syrian President Bashar Assad has emerged in the U.S. media, granting an interview to CBS' Charlie Rose, which will be aired Monday. While the network did not release direct quotes from the exchange, Rose said Sunday on "Face the Nation" that Assad denied having anything to do with the chemical weapons attack that has the world on edge.

"He does accept some of the responsibility" for the attack that killed almost 1,500 Syrian civilians - including hundreds of children, Rose said. "I asked that very question: 'Do you feel any remorse?' He said, 'Of course I do,' but it did not come in a way that was sort of deeply felt inside. It was much more of a calm recitation of anybody who's a leader of a country would feel terrible about what's happened to its citizens."