Over the past decade, President Trump has steadily expanded executive power, pushing the limits of his authority and evading traditional constraints. But a Democratic takeover of Congress on Tuesday could set up one final constitutional test for the Trump era, challenging the legislative branch to reclaim its role as a check on an increasingly powerful White House. A blue wave could give Democrats control of both chambers of Congress, handing them not only investigative and subpoena powers in the House, but also, through the Senate, the authority to confirm presidential appointments, pursue impeachments trials, and control legislation and federal spending.

That would historically be enough to bring a president to heel. Yet the Trump administration's broad assertion of executive privilege and politicization of the Justice Department could make oversight from a Democratic Congress sluggish — if not impossible — over Trump's final two years. The Office of Legal Counsel has claimed that even Trump’s communications with private advisors could be shielded by privilege. Independent watchdogs across the federal government, which have traditionally supported congressional oversight, have been systematically removed.

And a Justice Department that historically pursued congressional criminal referrals regardless of their political implications is poised to ignore them under current leadership. A combative administration will pose a challenge to Democratic congressional leaders, who may face internal party calls to pursue a third impeachment of the president over any number of scandals, and will likely shape debate over the coming presidential campaign season. "Our system of checks and balances and the requirements of super majorities makes it difficult for the legislature to hold the executive fully accountable," said Alan Dershowitz, a professor emeritus at Harvard and a lawyer to Trump during his first Senate impeachment trial.

"This is a good thing," he added, "leaving ultimate accountability to the voters, who are the ultimate check in a democracy."

Norm Eisen, who served as chief ethics lawyer for President Obama and counsel for the House Judiciary Committee during Trump’s first impeachment trial, acknowledged the Trump administration is likely to aggressively resist Democratic probes. "To be sure, those in the government may resist," Eisen said, "but the incredible scale of corruption over the past 20 months has also implicated a wide variety of those in the private sector. They will cooperate because the consequences for not doing so are too great."

Democratic control will also challenge the expansive vision of presidential power that Trump and his closest aides have successfully advanced since the 2024 campaign. Project 2025 — a conservative effort pioneered by Trump allies that ultimately joined the administration — embraced a sweeping theory of unitary power, under which the president would exercise near-total control over the executive branch, including the Justice Department. A conservative Supreme Court, featuring three Trump appointees, has endorsed key elements of that theory, affirming broad presidential authority to remove executive officials and granting presidents absolute immunity for exercising their core constitutional powers, along with presumptive immunity for other official acts.

Practical limits on the oversight powers of a Democratic Congress already has some leaders thinking of other, coercive means of using congressional power to exact accountability. A cabinet fleeing for the campaign trail, or for the safety of the private sector, may create a series of openings that will be difficult for Trump to fill with a Democratic majority in the Senate, said Andrew Rudalevige, a professor of government at Bowdoin College and author of “The New Imperial Presidency.”"Trump doesn't have a huge legislative agenda, but there are some things he wants," Rudalevige said.

"Those can be held up. And relatedly, Democrats could embrace the power of the purse, since the budget is the one bill that needs to pass." Already, several Democratic House members are debating whether to demand the resignation of Pete Hegseth, Trump's embattled defense secretary, as a condition of further appropriations funding for the department in its pursuit of war with Iran, the Hill first reported last month. Democrats may find it difficult to hold the administration accountable for past actions, much of which are already being litigated in federal courts, said Peter Kastor, history department chair at Washington University in St. Louis.

The larger question, he said, is how the two parties could govern together — particularly if Trump defies congressional authority, such as by impounding funds appropriated by lawmakers. "I think it will be extremely difficult for Democrats to take any action to punish the administration for its actions until now, much as Democrats may want this," Kastor said, suggesting the greatest wild card may lie not in Democratic strategy, but in the actions of a Republican minority. "The big question is not whether they will desert Trump," he added, "but rather what role they would see for themselves as a minority caught in the middle of a grand political battle."

In an interview with the New York Post, Trump suggested he is expecting a wave, stating he will "become Mr. Veto" if Democrats sweep control. But a president who long viewed concession as weakness may now have to pivot. "At some point, we’ll probably make deals," he added.