During a campaign swing through Iowa over the weekend, Sen. Bernie Sanders (I-Vt.) questioned Democratic presidential frontrunner Hillary Clinton's relative silence on trade policy.

Sanders' three-day trip to Des Moines, Cedar Rapids, Waterloo and elsewhere came as House Democrats abandoned President Barack Obama on Friday and helped kill legislation that would give him greater power to negotiate a 12-nation trade deal known as the Trans-Pacific Partnership. While Sanders has long opposed the TPP, Clinton has attempted to remain above the fray.

"I am not clear, nor do I believe the American people are clear, as to what Secretary Clinton's position is," Sanders told reporters in Indianola on Sunday, according to the Washington Post. "Is she for it or is she against it? Those are your two options. The president is for it. Most Democrats in the Congress are against it."

Earlier Sunday, Sanders took that message to CBS' "Face the Nation." 

"I would hope very much that Secretary Clinton will side with every union in this country, virtually every environmental group, many religious groups, and say that this TPP policy is a disaster, that it must be defeated, and that we need to regroup and come up with a trade policy which demands that corporate America start investing in this country, rather than in countries all over the world," the senator told CBS' John Dickerson. 

Clinton did weigh in on the matter Sunday during her own rally in Des Moines. Though she did not indicate whether she supported giving Obama fast-track authority, Clinton argued that any trade deal must protect American jobs, wages and national security.

"No president would be a tougher negotiator on behalf of American workers, either with our trade partners or Republicans on Capitol Hill, than I would be," she said, according to CNN.

According to local and national press reports, more than 700 people showed up to hear Sanders speak at Drake University Friday night in Des Moines. On Saturday, the Vermont independent hosted an open house at his new Iowa campaign headquarters in Des Moines. It's the first campaign office Sanders has leased outside of Burlington, Vt., and Washington, D.C.

Sanders used the opportunity to introduce four new staffers, who join Iowa campaign director Pete D'Alessandro on his Hawkeye State team: Iowa political director Blair Lawton, state field director Justin Huck, state operations director Tara Thobe and college outreach director Evan Burger.

Lawton previously served as Iowa field director for the recently disbanded Run Warren Run, a group that tried, without success, to convince Sen. Elizabeth Warren (D-Mass.) to run for president. Last month, Sanders hired the group's New Hampshire state director, Kurt Ehrenberg, to lead his Granite State operations.