FIRST ON FOX: Sen. Chris Coons, D-Del., blasted the left-wing activists who recorded Sen. Kyrsten Sinema, D-Ariz., in a women’s restroom, saying it was "not at all" appropriate.

Coons caught up with Fox News in a Tuesday phone interview where he discussed President Biden's Build Back Better agenda.

Sinema has become a key figure in the Democrats’ fight to get Biden’s agenda across the Senate finish line, joining West Virginia Sen. Joe Manchin, a fellow Democrat, in pushing for a moderate approach to the spending bills.

SINEMA CONFRONTED IN AIRPORT FOR SECOND TIME THIS MONTH, ‘DON’T TOUCH ME’

Because of her unflinching moderate stance on the bills, Sinema has endured progressive protesters accosting her in airports and, most notoriously, following her into a women’s restroom at Arizona State University (ASU) while filming her.

Coons, who replaced the president in the Senate when Biden was elected vice president, torched the protesters for their actions, telling Fox News that it was "not at all" appropriate for them to follow Sinema into the bathroom with their cameras rolling.

Sen. Chris Coons, D-Del., condemned left-wing harassment of Sen. Sinema 

"Look, accountability to our constituents, openness to the views of those we represent is an integral part of public service," Coons said, adding that "harassing, intimidating, even abusing other folks" crosses the line.

Coons noted that he spoke with Sinema about the bathroom confrontation, saying that "one of the things she was most upset about was that her students" at ASU were "also hounded and yelled at and filmed… in a women’s restroom."

The senator also recalled that Sinema told him her students "were scared by the incident" and that campus security was "taking action" against the protesters who targeted Sinema’s students.

"Harassing and intimidating elected officials isn’t a constructive way to try and get them to change their mind on a position," he said. "But, frankly, going after others, students of Sen. Sinema's who have nothing to do with her policy positions, I think was a misstep."

U.S. Sen. Kyrsten Sinema, D-Ariz., has repeatedly been confronted in public by left-wing activists   (Photo by Michael Brochstein/Sipa USA)

A video on Monday showed Sinema being confronted on the president’s agenda by a woman claiming she was a constituent, and the senator reportedly telling the woman not to "touch" her.

Coons also gave an update on the president’s Build Back Better agenda, telling Fox News that he is "optimistic" that Congress "will ultimately pass a bill that makes significant investments in things that impact the costs faced by average families."

"Things like pre-K and child care and elder care and prescription drug costs," Coons said, echoing the Biden administration’s claim that the multitrillion-dollar agenda is "fully paid for so we don’t increase the deficit."

"And that’s, I think, a positive agenda. Something that, if we deliver on it, will impact the lives of tens of millions of Americans in a positive way," Coons continued.

Sen. Chris Coons, D-Del. (AP)

The Delaware senator also revealed that he was in talks with Sinema and Manchin "literally today" regarding the Build Back Better agenda, saying that he believes the pair will support the agenda if they are "approached in a constructive and respectful way."

Fox News also pressed Coons on the filibuster – a source of contention between progressives in the Senate and both Manchin and Sinema, who have remained steady in their support of the rule.

Coons said he has worked to "advance bipartisan solutions" during his decade in the Senate and that he is open to changing the filibuster, but that outright nixing the measure wasn’t something he supports at this time.

"I’m open to discussing changes to the filibuster… I’m not there yet on voting to end the filibuster in every circumstance and for every purpose," Coons said.

Manchin and Sinema remain the linchpin for the Democrats to get the president’s agenda across the finish line in the Senate.

CLICK HERE TO GET THE FOX NEWS APP

Coons has been a stalwart supporter of the president’s Build Back Better agenda since Biden took office at the beginning of this year.

The hefty price tag on the agenda, however, has turned Republicans – as well as Manchin – off from the plan.

Houston Keene is a reporter for Fox News Digital. You can find him on Twitter at @HoustonKeene.