President Obama on Tuesday secured what he hopes will be the final Senate votes needed to block passage of a Republican-led resolution of disapproval against the landmark Iran nuclear deal, as Congress returned from recess to face a complicated fall schedule that also includes efforts to prevent another government shutdown.
First on the agenda this month is the internationally endorsed Iran pact, which has divided an already partisan Congress.
Four more Democratic senators announced their endorsement Tuesday, creating a 42-vote firewall of support, even though it remains unclear whether all Democrats will agree to filibuster the resolution and prevent a final vote on it from taking place.
Sens. Richard Blumenthal of Connecticut, Maria Cantwell of Washington, Gary Peters of Michigan and Ron Wyden of Oregon, announced they will back the deal. Obama had already locked up votes to sustain his threatened veto of the disapproval resolution in the House and Senate.
The new Democratic support could now deny deal opponents the 60-vote filibuster threshold needed to advance the measure, preventing the president from having to use his veto pen.
But some Democrats in the Senate have spoken publicly about the importance of holding a final vote, leading some to predict they may refuse to support a Democratic filibuster, even though they plan to support the president and the deal.
If the resolution crossed the filibuster hurdle, final passage would then only require a simple majority. The White House was pushing them to hold firm.
"We certainly would expect that those members of Congress who support the agreement to take the necessary steps in Congress to prevent Congress from undermining the agreement," said White House Press Secretary Josh Earnest, noting that 60 votes are "required to do just about anything in the United States Senate."
Senate Majority Leader Mitch McConnell (R-Ky.), however, warned senators against a filibuster, knowing that pushing Obama into a veto fight would be an embarrassing setback for the president and an outcome the White House hopes to avoid.
"This debate should not be about a president who will leave office in 16 months. It should be about where our country will be," McConnell said as he opened the chamber after a four-week summer recess. Senators are "entitled to an up or down vote — not a filibuster or artificial limits on passage, but an important vote — on this resolution."
The partisan split will be on full display this week as proponents and opponents take their voices to the Capitol steps. Texas Sen. Ted Cruz and fellow Republican presidential hopeful Donald Trump will rally against the Iran deal on Wednesday. On Tuesday night, House Democratic Leader Nancy Pelosi plans to welcome military families in a show of support.
Supporters say the accord is the best hope for stopping the Iranian regime's pursuit of a nuclear bomb, but opponents, led by the pro-Israel American-Israel Public Affairs Committee, argue a better deal could have been reached.
Many Democratic lawmakers have struggled with their decisions, but both the House and Senate are expected to give the president the two-thirds majority needed to uphold his veto. Pelosi also scooped up more backers Tuesday.
"I do not believe that supporting this deal will prevent Iran from eventually acquiring a nuclear weapon," Sen. Joe Manchin III (D-W.Va.) said Tuesday, becoming the fourth Democratic senator to announce his opposition to the deal.
Senate Minority Leader Harry Reid (D-Nev.) has offered to forgo the filibuster and move directly to a final vote as long as Republicans agree to require at least 60 votes for passage rather than 51. But lacking those votes, McConnell declined that offer Tuesday.
The House is set to vote Friday, and the Senate will likely finish next week before a self-imposed Sept. 17 deadline.
The Iran votes top a charged fall agenda that includes a budget showdown and a historic visit from Pope Francis that is expected to draw hundreds of thousands of faithful to the Capitol.
After the Iran deal votes, Congress then has just two weeks to agree on legislation to fund the government and prevent a federal shutdown Oct. 1.
Cruz and other lawmakers are vowing a fight to defund Planned Parenthood after disclosures that the organization donates fetal tissue from abortions for research.
Planned Parenthood is already banned from using federal funds for abortions, except in limited cases of rape, incest or a threat to the life of the woman. But lawmakers want to cut off the money it receives for routine family planning services, including birth control and disease screenings.
The funding fight may resemble the 2013 battle led by Cruz over the Affordable Care Act, which resulted in a 16-day federal government shutdown that bruised both parties, but particularly the GOP.
In between the two top debates, lawmakers will welcome Pope Francis for the first-ever address by the leader of the Roman Catholic Church to a joint meeting of Congress.