House Democrats’ plan for the impeachment inquiry is simple: focus exclusively on President Trump pressing his Ukrainian counterpart to discredit Joe Biden. But the pace of new revelations, like Trump openly calling for China to collude with him, is testing that strategy, and prompting some progressives to wonder if it’s a mistake to ignore Trump’s interactions with other foreign leaders.

With the inquiry not even two weeks old, and reluctantly undertaken by House Speaker Nancy Pelosi (D-CA), many House Democrats worry that an expansive focus will distract from the straightforward account, presented in a whistleblower complaint and confirmed by a call summary released by the White House, that Trump urged Ukrainian President Volodymyr Zelensky to investigate political rival Biden.

Most lawmakers have backed up Pelosi’s keep-it-simple strategy. “I think we should be focused, not overthink this,” said Rep. Eric Swalwell (D-CA) last Thursday. “Right now, people understand what he did.”

And staffers for members around the Democratic caucus indicated support for a narrow inquiry focused on Ukraine. “Arguably, the stronger case you have to send to the Senate is what you want,” said one Democratic aide, “but they’re already so slow moving on one topic, so to add in more… I think there could be enough with Ukraine to do what needs to get done.”

That calculus grates on some progressives, even if they may be outliers on the Hill. One congressional aide said it was “malpractice” for the Democrats to keep a narrow impeachment focus, as Trump is “blatantly using our country’s foreign policy as a tool for his own domestic political benefit.”

“In the particular case that triggered the impeachment inquiry, it was Trump pressuring the Ukrainian president to help gin up something against Biden, but we know he’s brought this kind of pressure before,” the aide continued. “In the case of pressuring [Israeli Prime Minister Benjamin] Netanyahu to ban two members of Congress, he did it right out in the open. So it would frankly be malpractice for Congress not to seek records of other calls to determine what pressure may have been brought to bear by Trump against other foreign leaders to achieve political and possibly financial benefits for himself.”

A Senate Democratic staffer agreed. “I don’t understand why House Democrats would limit themselves to Ukraine given that the president laid out his own blueprint for what Democrats should investigate. Just today it’s China, but now his attorney general is pressing U.S. allies like the Five Eyes [surveillance] alliance to work on behalf of his political agenda undermining the Mueller Report.”

The staffer said Senate Democrats weren’t much better: “I don’t think Senate Democrats have been particularly brave or outspoken for a broad impeachment inquiry, either.”

Neither the news cycle nor the president is cooperating with the Ukraine-centric strategy, which may stretch current Democratic patience. New revelations that the president pressed foreigners to aid him in discrediting his domestic political opponents accumulate almost daily. This week alone, they’ve expanded to include Australian Prime Minister Scott Morrison and British Prime Minister Boris Johnson. Then, on Thursday morning, Trump openly said that “China should start an investigation into the Bidens,” something Biden campaign aide Kate Bedingfield likened to Trump’s 2016 call for Russia to steal Hillary Clinton’s emails.

All that is eclipsing behavior that earlier in Trump’s presidency was seen as abuses of power, such as a foreign government reportedly booking multiple rooms in Trump hotels for a single guest or aiding the rehabilitation of Saudi Crown Prince Mohammed bin Salman after the CIA assessed him as responsible for murdering journalist Jamal Khashoggi.

The recent revelations have raised questions about how standard it is for Trump to solicit personal favors while ostensibly conducting presidential business. And before the Ukraine revelations emerged, several House Democrats wanted Trump impeached for using his office to enrich himself, a violation of the Constitution’s emoluments clause.

A congressional source said the House Foreign Affairs Committee intends to stay focused on Ukraine at present but didn’t rule out expansion in the future. A representative for the House Intelligence Committee declined to comment, and those from the House Oversight Committee didn’t respond to requests for comment.

Yet by Wednesday, the two committees took a step to expand the probe. Listed among materials the committee chairs plan to subpoena from the White House are communications between Trump “and the leader of any other foreign country” relevant to “pursuing investigations of President Trump’s political rivals and Ukrainian foreign aid.” Asked if the inquiry would expand to scrutinize conversations with other foreign leaders, a congressional source said “it may be trending in that direction,” as each of the “new stories hit all the same notes.”

Presidential communications with foreign counterparts are typically considered privileged and beyond the scope of Congress. The subpoena, which Democratic leadership anticipates formally issuing Friday, already tests that and is likely to lead to litigation in order to enforce it. That outcome is uncertain enough before any potential expansion into non-Ukraine communications.

Scott Cullinane, a former staffer on the foreign affairs committee, warned that going after Trump’s other communications with foreign leaders risked setting precedents that would come back to haunt both Democratic and Republican presidents.

“The Executive Branch has a legitimate need for confidential conversations as a part of effective American diplomacy. Congress has an oversight responsibility, but overreaching has consequences that will outlast any one administration,” Cullinane said. “It could affect how any future president conducts foreign policy and change how foreign leaders share information with the U.S. government.”

And any effort to expand the scope of the impeachment probe, however incremental, is likely to meet stiff resistance among the dozens of House Democrats, largely from swing districts, who recently came out in favor of an impeachment inquiry and are bracing for its political impact.

Though they acknowledge additional findings could be explosive, these Democrats worry about a drawn-out effort to obtain records of more Trump calls—which would probably be decided through the courts—extending into next year and snarling the prospects for bills they’re holding out hope to pass on health care and infrastructure. Pelosi is clearly proceeding with their concerns top of mind, and her team is taking pains to hear out moderates worried about impeachment becoming a 2020 liability.

At a town hall on Wednesday night, Rep. Susan Wild (D-PA), who was an impeachment holdout before the Ukraine allegations broke, argued Democrats should keep the inquiry limited—a view echoed by many of her colleagues who also flipped GOP-held districts in 2018.

“I have an interest in keeping it as narrow as possible,” she said. “I don’t want this to be another Benghazi.”

—Erin Banco contributed reporting