Congress returns Tuesday to face several key decisions and short-term deadlines -- including votes on the Iran nuclear deal and a spending bill that if connected to efforts to defund Planned Parenthood creates the potential for another government shutdown.

The House and Senate could vote as early as this week on the Iran deal. 

Both GOP-controlled chambers are expected to pass motions of disapproval for the deal. But President Obama is expected to veto the motions and ultimately complete his historic foreign policy deal because neither chamber has the two-thirds majority to override the presidential veto.

Republicans argue the deal, in which Iran will curtail its nuclear development program in exchange for the easing of billions of dollars worth of economic sanctions, gives too many concessions to the rogue nation.

GOP leaders are playing down talk of a government shutdown that's being driven by conservative lawmakers determined to use the spending legislation to strip funds from Planned Parenthood.

Senate Majority Leader Mitch McConnell, in fact, suggested last week that such an effort is pointless because Obama would reject any such bill.

“The way you make a law in this country (is) the Congress has to pass it, and the president has to sign it,” McConnell told WYMT-TV, in his home state.

“The president's made it very clear he's not going to sign any bill that includes defunding of Planned Parenthood -- so that's another issue that awaits a new president hopefully with a different point of view.”

The president must sign a stopgap spending bill by Sept. 30 to keep the federal government fully operational.

Still, Texas GOP Sen. Ted Cruz, a 2016 presidential candidate and one of Congress’ most conservative members, appears to be going ahead with a defunding effort, asking McConnell not to schedule a vote on the issue.

Republicans were blamed for the Cruz-led partial shutdown in 2013 over ObamaCare, but neither party wants to risk being blamed for another one in a presidential election year.

Planned Parenthood is under intense scrutiny after secretly recorded videos raised uncomfortable questions about its practices in procuring research tissue from aborted fetuses.

The first days for Congress, after a roughly eight-week summer break, also are expected to include efforts to increase the government's borrowing authority and avoid a first-ever federal default.

Members also will try to reach a deal on a long-sought highway bill, consider extending roughly 50 tax breaks, pass a defense policy bill that Obama has threatened to veto and renew the Federal Aviation Administration's authority to spend money.

House GOP leaders are expected to try to strip Planned Parenthood of its federal funding without creating the possibility of a shutdown, as Pope Francis plans to speak on Capitol Hill on Sept. 24.

They have been considering separate legislation this month cutting Planned Parenthood's funds, a GOP aide and a lobbyist said.

The leaders hope such a bill, which would advance free of a filibuster threat by Senate Democrats, would satisfy Planned Parenthood's opponents and free up the temporary government funding bill.

Obama would almost certain veto that bill, too. But it would allow Republicans to vote for the changes and make a case for electing a GOP president to institute them.

Facing demands for negotiations to lift domestic agency budgets hit by the return of automatic spending cuts, known as sequester, McConnell has signaled that he is open to talks on a deal that would pair increases for domestic programs with budget relief for the Pentagon.

To get to an agreement, however, Republicans must strike a deal with Obama and his Democratic allies over companion spending cuts elsewhere in the budget to defray the cost of new spending for the Pentagon and domestic programs.

There's a limited pool of such offsets, at least those with an acceptable level of political pain, and considerable competition over what to spend them on.

For instance, McConnell helped assemble a 10-year, $47 billion offsets package to pay for a Senate bill with small increases for highway and transit programs. Democrats are eyeing the same set of cuts to pay for boosting domestic agencies.

No one is underestimating the difficulty in reaching an agreement.

Speculation is growing that Republicans will try to advance a bill that would keep most federal agencies operating at current budget levels, with only a few changes for the most pressing programs. The White House has pledged to block that idea.

One potential glimmer of hope for the talks is that earlier this year Republicans reversed a position they held in talks two years ago and declared that additional defense spending doesn't require companion spending cuts.

Congress also needs to raise the government's $18.1 trillion borrowing cap by mid-November or early December, an uncomfortable prospect for GOP leaders already facing potshots from Tea Party purists and Republican presidential candidates as next year's nomination contests loom.

The Associated Press contributed to this report.