WASHINGTON — When President Donald Trump's lawyers were in court this summer trying to block a congressional subpoena for Trump's financial records, they argued that House Democrats hadn't given a valid reason for demanding the documents.

It's not like the House was pursuing impeachment, they repeatedly pointed out. That, they argued, would be a very different situation.

Now that Speaker Nancy Pelosi has officially announced that House Democrats are, in fact, pursuing an impeachment investigation, Trump’s argument will likely be a tougher sell with judges — and Democrats could try to use it against him. Trump's lawyers didn't outright concede that Democrats could lawfully subpoena Trump's records if it was part of an impeachment inquiry, but they suggested it might be a closer call.

Pelosi’s announcement raises the stakes in court fights that are already underway over House Democrats’ efforts to gather documents and force testimony on the Russia investigation as well as the president’s personal financial dealings. The limited number of past court decisions about the scope of Congress’s power in these situations makes it hard to predict how adding impeachment to the mix will affect things going forward.

Kerry Kircher, who served as general counsel for the House of Representatives from 2011 to 2016, when Republicans were in the majority, told BuzzFeed News in an email that Pelosi’s announcement strengthened Democrats’ position.

“One of the arguments that Trump, [Treasury Secretary Steven] Mnuchin and others opposed to the House's efforts to enforce its subpoenas have made in court is that the subpoenas lacked a legislative purpose. That was never a good argument to begin with, but now it just disappears,” Kircher wrote. “[A]t least as of now, the impeachment inquiry has been defined to include all of the existing committee investigations into Trump's conduct which are the investigations that generated the subpoenas at issue.”

There are almost certainly more subpoena fights to come. House Democrats are just starting to probe a July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky, in which Trump asked Zelensky to investigate former vice president Joe Biden as well as the origins of the investigation into Russian interference in the 2016 election. The political maelstrom over the Ukraine call prompted Pelosi’s impeachment announcement, although the House committees are free to continue to pursue other investigations.

Looking for guidance in past presidential subpoena fights about whether an impeachment investigation will make it easier for Congress to pry information from Trump and those around him doesn’t offer easy, apples-to-apples comparisons. There is no independent counsel, like there was when President Bill Clinton was under investigation, and there is no separate grand jury investigation (at least not that anyone is aware of), like there was when President Richard Nixon was under investigation.

Pelosi also didn’t announce the creation of a special committee to investigate the president, which happened under both Clinton and Nixon. She instead put her support behind House committees that are already investigating the president. The House Judiciary Committee is in court fighting to get grand jury materials related to the Russia probe, and told a judge that request was related to a potential impeachment investigation. The Judiciary Committee is also suing to enforce a subpoena for testimony from former White House counsel Don McGahn.

Trump has filed lawsuits to block subpoenas issued by the House Oversight Committee, House Intelligence Committee, and the House Financial Services Committee for his financial records. The president is also in court challenging a New York law that would give the House Ways and Means Committee a way to get his tax returns. The Ways and Means Committee, meanwhile, is suing to enforce a subpoena to the Treasury Department for Trump’s tax returns.

Irvin Nathan, who served as general counsel for the House from 2007 to 2011, when Democrats were in charge, said there was no law that subpoenas issued as part of an impeachment investigation should get greater weight. But he also said that Trump was wrong to argue in the first place that a committee’s reason for issuing a subpoena — impeachment or otherwise — mattered, as long as it was a “valid” function.

Pelosi’s impeachment announcement could help Democrats get the Mueller grand jury materials, though, since impeachment was considered a “judicial” function that could trigger an exception to grand jury secrecy, Nathan said. Democrats could also invoke pending impeachment proceedings in asking judges to move quickly to resolve subpoena fights, he said.

Trump’s legal strategy so far in fighting congressional subpoenas has been to argue that Democrats lacked a “legitimate legislative purpose” in subpoenaing him. In a legal brief filed in June in the US Court of Appeals for the DC Circuit in a case about the House Oversight Committee’s subpoena to Trump’s accounting firm Mazars USA LLP, Trump’s lawyers drew a line between Congress’s “legislative” functions and its “non-legislative” powers, such as impeachment or punishing members for misconduct.

“While Congress could presumably use subpoenas to advance these non-legislative powers, the Committee has not invoked them,” Trump’s lawyers wrote at the time. “The Mazars subpoena has nothing to do with internal House discipline, and the Committee has never tried to defend it under the House’s impeachment authority.”

Impeachment, Trump's lawyers wrote, was "a weighty constitutional matter with grave political ramifications." They tried to distinguish between the congressional investigations into Nixon and Clinton — which "quickly morphed into impeachment proceedings," they noted — and the congressional investigations into Trump at the time.

Trump’s lead attorney, William Consovoy, declined to comment.

The US Supreme Court has ruled that sitting presidents aren’t automatically immune from investigation and that courts can weigh in when presidents invoke executive privilege — that decision came in 1974, when the court ruled 8–0 that Nixon wasn’t immune from a grand jury subpoena for tapes he had recorded in the White House. The case involved a pending criminal investigation, though, not a congressional subpoena.

Lower courts have largely rejected efforts by previous administrations to argue that judges can’t get involved at all in subpoena fights between Congress and the executive branch. During the Obama administration, a federal judge in Washington, DC, found that she had the power to decide if the administration properly invoked executive privilege to shield Justice Department documents from House Republicans. During the George W. Bush administration, a judge ruled that senior administration officials weren’t covered by absolute immunity when faced with House Democrats’ subpoenas to testify.

During the Watergate investigation, the DC Circuit did rule in a subpoena fight between Nixon and a special congressional committee established to investigate him. The Senate Select Committee on Presidential Campaign Activities had subpoenaed tapes that Nixon recorded, and Nixon refused to comply, claiming executive privilege. The appeals court in 1974 blocked the subpoena, finding the committee had failed to show that its “legislative” purposes in trying to get the tapes wasn’t strong enough to overcome the president’s need for confidentiality.

In the Mazars case, a federal district judge sided with House Democrats in May. US District Judge Amit Mehta wrote that even absent a formal impeachment investigation, it was “simply not fathomable” that Congress would have the power to remove a president but lack the power to investigate potential unlawful activities.

On appeal, Trump’s lawyers argued that Mehta was wrong to bring up impeachment when Democrats hadn’t said that was the reason for the subpoena. They cited the 1974 DC Circuit case in their DC Circuit brief in June, noting that the court at the time distinguished between the select committee’s “legislative” purpose and the needs of the grand jury and the House Judiciary Committee, which was carrying out an impeachment inquiry into Nixon at the time.

The DC Circuit heard arguments on July 12 and has yet to rule.