Democrats will wield subpoena power if they can flip the House this fall.

They're already prepared to compel top officials such as White House senior adviser Jared Kushner, EPA head Scott Pruitt, and White House counsel Donald McGahn.

It could be the most consequential change if control of the House changes parties.

If Democrats retake the House this fall, there's a power they will gain that could suddenly become the centerpiece of the party's attempt to serve as a check on the president — and it has nothing to do with impeachment.

It's the subpoena power Democrats will wield should they reclaim the majority.

On a number of committees, such as the House Committee on Oversight and Government reform, Democrats will simply resend the letters requesting documents that they've addressed to officials such as White House senior adviser Jared Kushner, White House counsel Donald McGahn, and Environmental Protection Agency Administrator Scott Pruitt — only they would then be compelled to appear before the committee and provide documents under the weight of a subpoena.

Failure to comply could then lead to criminal penalties.

One Democratic House staffer said Democrats gaining the subpoena power would be of the utmost importance.

"It may be the most important thing people aren't thinking about right now," the staffer told Business Insider. "Trump himself will be the most impacted, because he hasn't had to face vigorous oversight, and even so a lot of his wrongdoing has emerged via leaks and reporting. If Congress starts looking with the force of law at its back, who knows what we might turn up?"

The staffer predicted "you could see a lot of departures of high-profile people if we win the House" as a result.

"Just a suspicion but it has strong historical precedent," the staffer went on. "If we have the Oversight Committee, I think you'd see much more regular testimony by every member of the Cabinet, and more testimony from subordinates where there is something really bad happening," such as security clearance issues or the travel habits of Cabinet officials.

'It could effectively paralyze the entire Trump administration'

A second Democratic staffer, who works on the Oversight Committee, seconded those sentiments. The staffer said that Democrats, should they flip the House, "would start this process is by insisting that the Trump administration finally start producing documents they have been withholding on a wide variety of topics."

"Democrats would hope subpoenas would not be necessary, but they would not shelve this critical oversight tool as Republicans have to date," they continued. (When asked about the Democratic charge that Republicans had shelved the subpoena tool during Trump's early years in office, a Republican committee staffer was quick to point to the zero subpoenas filed by Democrats when they last controlled the committee during the start of President Barack Obama's first term.)

Since Trump won the presidency in late 2016, Democrats on the committee have sent dozens of letters to various entities, the vast majority of which are seeking information from the Trump administration. On many of these, action has not been taken and could be revisited at the start of the next Congress. High-profile, televised hearings before the committee could become frequent.

Elijah Cummings. AP Photo/Patrick Semansky

"The Oversight storm will touch every person who works in the West Wing, every member of the Trump Cabinet, every department and agency within the federal government," Kurt Bardella, a former spokesman for the Republican-controlled Oversight Committee, told Business Insider. "It could effectively paralyze the entire Trump administration and have a far more systemic impact than even [special counsel Robert Mueller's Russia] probe."

Bardella, now a Democrat, served in his role on Oversight when Republican Rep. Darrell Issa, of California, chaired the committee. Bardella said that committee in particular will be central if Democrats retake the House because of the broad scope it has to probe the executive branch.

Bardella pointed to a February list that Democratic Rep. Elijah Cummings, the ranking member on the committee, sent to Republican Rep. Trey Gowdy, the committee chairman, of 13 subpoena motions he wanted to see the Republican majority act on. Some of those motions included compelling Kushner to provide emails that Cummings said were being withheld; compelling the Trump transition team and Department of Justice to provide documents on interim security clearances; and compelling the Trump Organization to provide documents detailing payments it received at its properties from foreign officials.

That list provides "a blueprint for the type of investigations we can expect should Cummings and his Democratic colleagues take control of the committee," Bardella said.

"In totality, these investigations could have a crippling effect on the functionality of the entire Trump administration," he said. "Oversight Democrats are targeting documents that touch every part of the Trump presidency."

Democrats are targeting a vast number of Republican-controlled congressional seats in hopes of flipping the House. The party needs to flip fewer than 30 GOP-held seats to reclaim the lower chamber of Congress, which looks well within the realm of possibility based on some recent federal electoral results. But a recent CNN poll showed that Republicans were gaining on Democrats in the generic ballot. After Democrats held a 16-point lead over Republicans in February, that lead was trimmed to just three points last week.