With the House of Representatives now under Democratic control and the gavel in Speaker Nancy Pelosi’s hands, some of President Trump’s critics are eagerly anticipating a surge of congressional investigations.
Democratic leaders have promised to scrutinize a host of issues, including Mr. Trump’s ties to foreign governments, his administration’s child separation policy, possible violations of campaign finance regulations and ethical lapses by his cabinet.
But some of the more extreme or coveted goals of Mr. Trump’s critics may not be imminent or even feasible. Here’s what Congress can — and cannot — do to investigate.
Impeaching the President
Impeachment clearly resonates with a majority of Democratic voters, and with some more zealous members of Congress. Democratic leaders, however, have been more cautious. Ms. Pelosi on Friday called impeachment “divisive” and suggested that dissatisfied voters should look to remove Mr. Trump in an election, rather than by impeachment.
Logistically, impeaching a president or other top government official involves two steps.
A majority of the House must first vote to approve articles of impeachment, which essentially serve as an indictment of the official and sets up a trial in the Senate. Then, two-thirds of the Senate must vote to convict the official to remove him or her from office.
To date, only two presidents have been impeached — Andrew Johnson and Bill Clinton. Both were acquitted in the Senate. According to the Congressional Research Service, of the 15 federal judges, one senator and one cabinet member whom the House has voted to impeach since 1797, the Senate convicted eight federal judges.
For those hoping that Congress might impeach Justice Brett M. Kavanaugh, there is even less precedent for impeaching members of the nation’s highest court than for the presidency. The House has only once voted to impeach a Supreme Court justice — Justice Samuel Chase in 1804 — and he was also acquitted by the Senate.
Mr. Trump, for his part, has cast impeachment proceedings as a political liability for Democrats. In a Friday tweet, he also again wrongly claimed that he is the most popular Republican president in history.
Obtaining and Releasing Tax Returns
Democratic leaders have said that obtaining Mr. Trump’s long-sought tax returns is a priority. Congressional tax-writing committees do have the authority to request taxpayer filings — including the president’s — from the Treasury Department, but there are a few hurdles that Democrats must first clear.
Representative Richard E. Neal, Democrat of Massachusetts and the chairman of the House Ways and Means Committee, has said that he would prefer that Mr. Trump release his tax returns voluntarily. Still, Mr. Neal cautioned to CNN that there was the possibility of a “a long and grinding court case.”
Rudolph W. Giuliani, Mr. Trump’s personal lawyer, has vowed to fight such a disclosure in court, arguing that Democrats have no legitimate reason to request the tax returns.
In a scenario that could pit the president’s personal interests against the government’s obligations, the Treasury secretary, Steven Mnuchin, told The New York Times in November that he would honor any legal requests from Congress to release the president’s tax returns.
Even if congressional Democrats do obtain Mr. Trump’s tax returns, they may face legal and political risks for releasing the documents to the public without his approval. The provision that grants congressional authority to request the returns allows committees to share the documents with the full House and Senate, but “only when sitting in closed executive session unless such taxpayer otherwise consents in writing to such disclosure.”
Jailing Those Who Refuse to Comply
Some Democratic voters, concerned by the possibility of witnesses ignoring congressional subpoenas, have raised the specter of jail time as a punishment or deterrent for noncompliance. But the road to such an outcome would be too long and cumbersome for effective oversight.
There are three methods by which lawmakers can penalize uncooperative people or compel cooperation.
First, the House or Senate can each try to imprison witnesses, but this process has been “long dormant,” according to the Congressional Research Service. It was last used in 1934 when Herbert Hoover’s commerce secretary was declared in contempt of the Senate for attempting to destroy subpoenaed materials; he was jailed for 10 days.
Congress can also refer a contempt case to the Justice Department for criminal prosecution. But prosecutors do not always pursue those cases.
In 1982, the Justice Department did not bring charges against Anne Gorsuch Burford, who was then the Environmental Protection Agency administrator, for refusing to cooperate with congressional investigators. Nor did similar refusals compel prosecutors to charge Joshua Bolten, the White House chief of staff, or Harriet E. Miers, the White House counsel, in 2008, or Attorney General Eric H. Holder Jr. in 2012.
Additionally, Congress can file a lawsuit in the United States District Court for the District of Columbia to enforce a subpoena. But this approach could lead to a protracted legal battle. For example, the case against Ms. Miers dragged on for 19 months and was ultimately dismissed.