WASHINGTON – After weeks on the campaign trail, presidential candidate and U.S. Sen. Ted Cruz will head back to the U.S. Capitol next week. With his return comes congressional anxiety — that Texas' junior senator could instigate yet another government shutdown. 

The U.S. House and Senate are staring down a Sept. 30 deadline to fund the government. Some conservatives are threatening to let that cutoff date pass unless the federal government stops spending any taxpayer dollars on Planned Parenthood. Given his high profile role in the 2013 government shutdown, Cruz is at the center of the speculation. 

He's done nothing in the last month to allay those concerns. 

At a South Carolina campaign stop in early August, Cruz would not rule out a shutdown. And in Houston last week, Cruz said: "Under no circumstances should the federal government be providing $500 million of your and my taxpayer money to fund what appears to be an ongoing criminal enterprise. We're going to have a battle." 

The push to defund Planned Parenthood at the federal level reached new heights in July when a conservative group released a string of undercover videos raising questions about the organization's practice of donating fetal tissue for medical research. 

Republican congressional leaders have insisted that a shutdown will not happen. But many on Capitol Hill are skeptical, drawing parallels to 2013, when the unsuccessful efforts of Cruz and other conservatives to defund the 2010 federal health care law helped lead to a 16-day shutdown.

The key difference this time? Cruz has an even bigger stage.

In a national poll released Thursday, Cruz was in a respectable third place in the GOP nomination race, but lagged far behind real estate magnate Donald Trump. It’s been a struggle for Cruz and every other candidate in the race to garner attention since the bombastic Trump announced his candidacy in June.

Some Republicans fear Cruz will use his Senate post to steal back some of the limelight, setting off fireworks in Congress in the fall to endear himself to presidential primary voters. Taking such a public stand on Planned Parenthood presents an opportunity to court the evangelical vote – a group on which Cruz is spending much of his political energy. 

If Cruz and his conservative allies have their way, any spending bill that extends government operations past the end of September would cut Planned Parenthood funding. A Cruz aide called the Planned Parenthood issue “a no brainer."

But Democrats are firmly behind the organization, and any such cuts in a must-pass spending bill are likely to be dead on arrival, either at the hands of a Senate filibuster or a presidential veto. 

Senate Majority Leader Mitch McConnell, a fellow Republican who has been at near-constant odds with Cruz, allowed a stand-alone bill to defund Planned Parenthood on the Senate floor in early August, and it failed after a filibuster. He has repeatedly insisted since that he would not allow a government shutdown over the spending bill.

Cruz’s fellow Texas senator, Senate Majority Whip John Cornyn, has echoed McConnell’s remarks.

Cruz is one vote — and he has little leverage in the Senate against the upper chamber's leadership. What he does have is influence over a group of conservative House members known as the “Tortilla Coast Caucus” — named after the Mexican restaurant where they met with Cruz during the 2013 shutdown. Often after those meetings, GOP House leaders would find their plans upended.

Assurances from Senate leaders have assuaged some concerned staffers on the Hill, along with the widely-held belief that the effort to defund Planned Parenthood lacks the organization and momentum behind 2013's efforts to defund the president's signature health care law. 

But others are bracing for the worst. Memories of 2013's furloughed staffers, upended schedules and plummeting poll numbers are still fresh.

Republicans bore the brunt of the blame for that shutdown. For a brief moment in late fall 2013, it appeared Democrats might even have a shot at retaking control of the House over it — and the Democratic National Committee experienced a burst of unexpected online fundraising. 

All of that political advantage quickly dissipated amid ongoing problems with the government's fledgling health care website.

Two years later, Democrats are readying their political firepower in the event of shutdown drama. The Senate Democratic campaign arm is already making the case against vulnerable Republican senators, preparing to hammer them if such a fight materializes.  

"As the specter of another Republican-fueled government shutdown looms, vulnerable Republican senators who have voted multiple times to defund Planned Parenthood will either shut down the government to get their way or be so terrified of their dismal re-election odds that they flip their vote in an attempt to salvage their chances," said Democratic Senatorial Campaign Committee spokeswoman Sadie Weiner. 

As for Cruz, he portrays Democrats as the extremists, willing to back Planned Parenthood at the expense of funding the federal government. 

"It shouldn't be lost on anyone who it is that is threatening a government shutdown," Cruz said in last week's Houston speech, referring to Democrats. 

"I think that's a profoundly irresponsible position," he added.   

Patrick Svitek contributed to this report.