Rarely has the executive branch been accused so often of violating—or outright ignoring—the will of Congress.

The Trump administration’s slow implementation of new sanctions against Russia has spurred the legislative branch to consider how to flex its muscles as Congress tries to act as a check on an executive branch that seems unwilling to carry out basic law enforcement.

“I really do think whether you’re the president of the United States or a United State senator or a Supreme Court justice, you take the oath that you take seriously to uphold the Constitution of the United States,” Sen. Ben Cardin (D-MD), the ranking member of the Senate Foreign Relations Committee, told The Daily Beast in a recent interview. “I know there’s a limit to the power of Congress—sometimes I’m disappointed there’s a limit, but there’s a limit to what power we have. There’s a limit to the power of the president of the United States.”

For months, a bipartisan group of senators has put pressure on the administration over its reluctance to move forward on enacting new sanctions against Russia. The law stipulating those sanctions—which President Trump was forced to sign in August after the legislation passed with overwhelming majorities in the House and Senate—has come under direct assault from the White House, dating back to the dog days of summer when it was first being crafted.

More recently, though, the Trump administration blew past an Oct. 1 deadline to issue guidance on how it would implement the sanctions, which will target individuals and entities in the Russian defense and intelligence sectors in retaliation for its election meddling and incursions into eastern Europe.

When lawmakers asked questions about the delay, they were left in the dark. It was only after Sen. Bob Corker (R-TN) pressed Deputy Secretary of State John Sullivan directly late last month during a phone call that the State Department belatedly issued guidance on how it would implement the sanctions—26 days after it was due. Corker—who has been locked in his own feuds and disagreements with Trump—got results. But it shouldn’t have even reached that point, lawmakers argue.

“I don’t accept the premise that the president can ignore Congress, and that we can’t enforce that,” Cardin said. “The president has a constitutional responsibility to carry out the laws that we pass. That’s a constitutional responsibility. And he’s violating the Constitution if he doesn’t carry it out.”

Cardin and Sen. John McCain (R-AZ), who chairs the Senate Armed Services Committee, have threatened procedural tactics including blocking Trump’s nominees to key foreign policy and national security positions. The reality, though, is that Congress is close to powerless in compelling the administration to act.

“While we may not be able to directly enforce it, I understand that we have limits as to how we can enforce. Congress doesn’t have a military that’s under our command,” Cardin added. “The president does. But we have purse strings that are under our command. And we could use that. We have a lot of power that we can exercise.”

Cardin, who helped craft the legislation, has previously suggested to The Daily Beast that the committee could also use the appropriations process to get the White House to come to the table. Cardin’s counterparts on the House Foreign Affairs Committee sent a letter to Trump demanding to know why his administration hadn’t acted by Oct. 1.

With more deadlines for sanctions implementation approaching rapidly, Cardin and McCain are keeping a close eye on the administration’s every move. After Corker stepped in, the State Department released a list of Russian defense and intelligence entities being targeted by the new sanctions regime. Countries and businesses who have financial relationships with those Russian entities will face sanctions if they do business with them after Aug. 2—the date President Trump signed the law. In the meantime, those countries and businesses can prove that they are terminating or winding down their financial relationships with the Russian entities. By Jan. 29, the administration must solidify which countries and entities are continuing to do business with those Russian firms, and are therefore subject to additional sanctions.

Micah Johnson, a spokeswoman for Corker, told The Daily Beast that the senator believes “State and Treasury are working in good faith to responsibly implement this important legislation.” Committee staffers were recently briefed on the implementation efforts.

But as the next deadline approaches, lawmakers aren’t optimistic that they’ll avoid having to publicly wrestle with the administration. Democrats and Republicans on the Senate Foreign Relations Committee have already questioned the president’s political will to fully enact the law. Cardin in particular airs his frustrations often.

“It’s called mandatory sanctions. It’s in the law. These are not discretionary. They’re mandatory,” Cardin lamented to The Daily Beast. “I don’t know what is not understood by the word mandatory. So we think we have taken away the discretion of the president in that regard. We are watching this closely.”

Beyond simple implementation, lawmakers have privately expressed concern that subsidiaries or third parties of the sanctioned companies might be able to skirt the punishments if they are not specifically listed, The Daily Beast has learned.

“We have raised this question with the State Department and continue to have conversations with them about how to track the issue to ensure that our sanctions regime is as strong as possible,” a Senate aide told The Daily Beast.

Lawmakers saw all of this coming, and they fought tooth and nail for a backstop in the law. The legislation contains a key provision that allows Congress to review any attempts by the executive branch to unilaterally ramp up or roll back sanctions—a measure intended as a backstop due to longstanding concerns over the president’s refusal to unequivocally accept the U.S. intelligence community’s assessment that Russia meddled in the 2016 election. Trump has referred to those probes—which are also focused on whether his associates colluded with Russian operatives—as “fake news” and a “hoax.”

To that end, the Trump administration has always been averse to the legislation. As The Daily Beast first reported, the government’s top sanctions enforcer was dispatched to Capitol Hill in July while the legislation was still being written to make the case that it should be significantly weakened—namely, that the congressional review provision should be scrapped entirely. That was a non-starter at the time for Corker, who led the effort that resulted in the bill passing the Senate 98-2, and in the House by a margin of 419-3.

With the veto-proof majorities in both chambers, Congress effectively forced Trump’s hand, leaving him no choice but to sign the bill. When he did so, though, he disparaged the measure as an example of congressional overreach, calling it a “seriously flawed” bill that contained “clearly unconstitutional provisions.” Trump claimed he “can make far better deals with foreign countries than Congress,” citing his business background.

There’s nothing new about a president complaining about Congress tying his hands behind his back. But taking those reservations to the next level in a way that sabotages the law altogether is a bridge too far for legislators already concerned with what they view as Trump’s blind spot on issues surrounding Russia’s election meddling.