"If you have an impeachment proceeding, Congress is at the zenith of its power," said Michael Conway, a former counsel to the House Judiciary Committee during Watergate.

The two big differences:

1) Grand jury material: The courts would be more likely to rule that Congress' need to see grand jury materials — the kind of references that were redacted in the Mueller report — overrides the federal rule that requires those materials to be kept secret.

• That's what happened during Watergate, Conway said, in a critical ruling by a federal judge that allowed the Judiciary Committee to see a grand jury report. (Conway wrote more about that ruling and others here.)

2) Legislative purpose: It would be harder for the Trump administration to win a court fight by arguing that Congress doesn't have a "legitimate legislative purpose," the reason Treasury Secretary Steven Mnuchin cited in his decision not to release Trump's tax returns to the House Ways and Means Committee.

• No one questions the congressional power to impeach, so launching an impeachment inquiry "removes whatever doubt a court might otherwise have about the existence of a legitimate Article I purpose for demanding information of limited facial relevance to possible congressional legislation," Harvard law professor Laurence Tribe wrote in an email.

The bottom line: None of this affects the political decision of whether it's wise for House Democrats to move ahead. Pelosi says it isn't, and so far most of the Democratic committee chairs are siding with her. But it's not clear how long they'll be able to resist the pressure.

Go deeper: Which House Democrats are calling for Trump's impeachment

How it works: Democrats on the House Appropriations Committee are writing the bills that will fund the federal government for the next fiscal year — including the ones that will fund the Justice Department and the Treasury Department, two of the departments that have been resisting subpoenas.

• A separate House committee could ask the appropriators to add a provision that would limit funds to a department that isn't complying with the subpoenas.
• A member of Congress could also try to attach an amendment to one of the appropriations bills when they reach the floor in June.

So far, there's no detailed plan. Axios spoke with several members of Congress and staffers involved in the talks, and as of now they say discussions have been preliminary.

• "We look at it as, 'Okay what's our recourse?' This is one of them. We also have contempt orders and fines," a senior Democratic leadership aide told Axios.
• A House appropriations committee aide said the tactic would probably be useful mostly as a threat, adding that "if Dems are trying to target swift compliance, this may not be the most effective option" given how long it takes to pass appropriations bills.

The bottom line: There's probably no oversight tool that won't lead to months of delays if the Trump administration is determined to resist House Democrats.

Go deeper: How Trump is stalling Democrats

• "The fact they are pushing for me to leave immediately is heartless and void of any decency and compassion," Mark Morgan wrote to Kevin McAleenan, the former acting commissioner of Customs and Border Protection who is now Trump's acting secretary of the Department of Homeland Security. "This is just wrong."
• "I am being removed in the name of politics — and politics at its worst. … I will not have them believe I willingly left under these circumstances," Morgan wrote in one of the emails to McAleenan.
• In a separate email, he wrote: "This is wrong on many levels. I have several questions but I need to process through a bit more."

The reason for Morgan's removal isn't clear from the emails, and no official reason was given at the time of his resignation. But the National Border Patrol Council — a union representing 16,500 border patrol agents that endorsed Trump in 2016 — opposed him at the time because of what they described as his lack of experience.

• A source familiar said Morgan's firing was Trump's doing, because the union's president, Brandon Judd, privately told Trump to get rid of him. (Judd has had an outsized influence over Trump's running of the Department of Homeland Security in relation to the relatively modest size of his union.)
• Oddly, Judd seems to have reversed himself and is now praising Morgan's experience — at least publicly. After Trump announced he wanted Morgan to run ICE, Judd told Politico that Morgan would be a good fit to run the enforcement agency, given his investigative background at the FBI.

Context: Morgan, a career FBI official, was selected to run the U.S. Border Patrol in the final months of the Obama administration. He was the first chief in the 93-year history of the agency who had never worked as a border patrol agent, per the New York Times.

• His appointment drew backlash from the Border Patrol union, which argued that an insider should have been given the position. It called Morgan "a disgrace" to the agency in a Nov. 2016 Breitbart op-ed.

However, in the two years since his firing, Morgan has praised Trump's hardline border policies in television interviews and congressional testimony — calling for more aggressive executive action on immigration and criticizing longstanding U.S. law and nationwide injunctions.

• Those appearances seem to have paid off, with Trump reportedly calling Morgan after seeing him on TV to applaud his performance, per the Washington Post.

Morgan and McAleenan also seem to have warmed to each other again. In yet another twist in their relationship, McAleenan threatened to quit after White House senior adviser Stephen Miller tried to force McAleenan to make Morgan the head of CBP instead of ICE director, the Washington Post reported Friday.

• Following former DHS Secretary Kirstjen Nielsen's departure in April, Morgan told Fox News that McAleenan should be the next DHS secretary, calling him "extremely intelligent."
• And McAleenan praised Trump's decision to select Morgan for ICE director, saying Morgan's "record of service is needed to address the crisis at the border. ... The depth of his experience will be an asset to the Department and I look forward to working with him."

Morgan told Axios in a statement: Serving the men and women at Immigration and Customs Enforcement is a privilege. ... I look forward to rejoining the DHS workforce and working hand-in-hand with our law enforcement partners and the interagency community to enforce our nation’s immigration laws and end the humanitarian and security crisis at our southern border.

• The White House and DHS declined to comment.