Lawmakers have just a week to find out who will blink in the big shutdown showdown over Obamacare, although that’s not the only issue on the agenda.

House Republicans will push through a debt ceiling increase tied to an assortment of GOP wish list items including another attempt to delay Obamacare, approval of the Keystone XL oil pipeline and spending cuts, while Senate Democrats will again try to pass an energy efficiency bill.

But those are sidelines to the main event: whether the government will shut down come Oct. 1.

After the House voted 230-189, almost entirely along party lines, to pass a continuing resolution funding the government at $986.3 billion and defunding Obamacare, Senate Democrats will maneuver to send a “clean” spending bill back to the House.

Senate Majority Leader Harry Reid, D-Nev., has vowed to block anything that defunds the health care law and President Barack Obama has vowed to veto it, even if the Senate were to somehow to pass it.

“I have said it before, but it seems to bear repeating: The Senate will not pass any bill that defunds or delays Obamacare,” Reid said last week.

That leaves two possibilities — Senate Republicans, led by Ted Cruz of Texas, may filibuster the House CR lest Reid use Senate rules to restore Obamacare funding with a simple majority. Such a gambit, which Cruz and other conservatives called for on Friday, risks a shutdown.

Perhaps more likely, Reid will find the 60 votes he needs to avoid a filibuster, amend the bill and send it right back to Speaker John A. Boehner, R-Ohio, who will then face the same pickle he did last week: Allow a vote certain to splinter his conference — or risk a shutdown over Obamacare that he has long maneuvered to avoid.

House Democrats would face their own decision, too, given that many say a bill that keeps sequester spending levels in place — even for a few more months — is unacceptable.

The House CR would keep the government running only until Dec. 15, setting up another potential showdown just before Christmas.

As leaders try to figure out precisely how to proceed on the CR, the Senate could buy time by continuing to debate an energy efficiency bill stalled indefinitely by non-germane Republican amendments.

Though a cloture vote on the stopgap spending bill would supersede the energy legislation, its co-sponsors — Democrat Jeanne Shaheen of New Hampshire and Republican Rob Portman of Ohio — likely will make noise about the Senate’s inability to pass any bipartisan bill, including their own. They likely do not want to move on to something new without a fight but, facing a government shutdown, they probably won’t have a choice.

“I want everyone in New Hampshire who is frustrated by gridlock and dysfunction in Washington to know that I share their frustrations. But I don’t plan on giving up and will continue to work to pass this bill,” Shaheen said Thursday. “I’m disappointed that a small group of senators have delayed action on a bipartisan effort to create jobs, lower pollution, and save taxpayers money.”

But in true Senate fashion, lawmakers could be trading gridlock on one issue for the next.

Meredith Shiner, Niels Lesniewski and Matt Fuller contributed to this report.