In this weekly column "Cross-exam," Elie Honig, a CNN legal analyst and former federal and state prosecutor, gives his take on the latest legal news. Post your questions below. The views expressed in this commentary are his own. View more opinion on CNN. Watch Honig answer reader questions on "CNN Newsroom with Ana Cabrera" at 5:40 p.m. ET Sundays. This article has been updated to reflect the latest news.

(CNN) Congress threw down the gauntlet Friday when it subpoenaed the White House for a broad set of documents relating to President Donald Trump's efforts to pressure Ukraine to investigate Joe Biden.

And today the Trump administration blocked a US ambassador from testifying to Congress in the Ukraine probe. The parties now are careening towards a Supreme Court showdown that could redefine the balance of power between the legislative and executive branches of government. And the outcome could rival in historical significance the 1974 decision that led to the resignation of President Richard Nixon.

The new House subpoena calls for essentially every White House document relating to Trump's July 25 call with Ukrainian President Volodymyr Zelensky, during which Trump laid it on the table: "I would like you to do us a favor though..." And the subpoena requires production of some documents stored on a highly sensitive electronic system where the transcript of that July 25 call was kept " lock[ed] down ."

This reportedly includes similar conversations with other foreign leaders. Watergate reporter Carl Bernstein compared these documents to the infamous White House tapes that led to Nixon's resignation.

Do not expect the White House to comply with the subpoena. Ever since Trump announced his "we're fighting all the subpoenas" strategy, his administration has held the line and defied congressional subpoenas. If anything, expect the White House to dig in even deeper now that its own most sensitive -- and potentially damaging -- information is at stake.

If the White House stonewalls, Congress can seek enforcement of the subpoena in court. Given the enormity of the stakes, Congress could try to get the case quickly to the Supreme Court under a rarely-invoked rule permitting direct review if the case "is of such imperative public importance as to justify deviation from normal appellate practice and to require immediate determination in this Court."

A legal dispute over the House's new subpoena seems destined for an all-in legal battle that will echo the monumental 1974 ruling , which required the White House to provide the Nixon tapes to the special prosecutor. The Nixon Court, by unanimous decision -- including three justices who had been appointed by Nixon (a fourth, future Chief Justice William Rehnquist, recused himself) -- ruled that while executive privilege existed, it did not extend to shielding Nixon from turning over the incriminating tapes. Nixon resigned just over two weeks later.

I see only two ways a decision on the Trump subpoena might come out differently. First, the Nixon Court held that executive privilege is not a general shield against criminal exposure but rather was intended primarily "to protect military, diplomatic, or sensitive national security secrets." So the court could find that the subpoena is at least partly invalid for that reason. But Congress might respond that Trump's efforts to dig up dirt on political enemies does not meet that description. Further, the White House itself already has voluntarily disclosed the summary transcript of the July 25 call, so how sensitive could it be?

Second, the Supreme Court's composition is entirely different today than in 1974. Five of the nine current Justices are Republican nominees with staunch conservative credentials -- including two Trump appointees, Justices Neil Gorsuch and Brett Kavanaugh -- though Chief Justice John Roberts has shown increasing signs of ideological independence and unpredictability.

If the case winds up in the Supreme Court, the future of the Trump presidency could hang in the balance. While Congress arguably already has enough to impeach -- the July 25 summary transcript, a damning series of recently-released texts between State Department officials and evidence of the White House effort to hide records of the call -- a decision enforcing the subpoena could open the floodgates, enabling Congress to discover the depth and breadth of the Ukraine scandal, and perhaps other similar incidents as well.

As much as Trump has defied traditional political expectations, it is difficult to imagine him surviving that.

Now, your questions:

Keith (Texas): The White House argues that the US House must hold a full vote before this is a valid impeachment inquiry. Is that right, and shouldn't House Republicans have the ability to subpoena materials and make their own arguments?

It its letter to House Democrats on Tuesday, the White House served notice of its blanket rejection of all Congressional subpoenas and information requests relating to the ongoing impeachment inquiry. Essentially, the letter memorializes under formal legal cover Trump's prior vow to "(fight) all of the subpoenas."

The White House's primary objection is that the full House has not voted to open an impeachment inquiry, rendering the inquiry -- as announced at a news conference by Pelosi, without any formal House action -- "constitutionally invalid and a violation of due process." The White House argues that the House has not established "even the most basic protections demanded by due process under the Constitution and by fundamental fairness," including the ability for Trump's legal team to cross-examine witnesses and to subpoena its own evidence.

Article I of the Constitution broadly grants the House the "sole power of impeachment." There is nothing in the Constitution, statute or prior judicial decision to indicate that a vote of the full House is required to start an impeachment inquiry. However, the full House did formally vote to initiate impeachment proceedings against both Presidents Richard Nixon and Bill Clinton.

The White House appears to have two primary strategic goals. First, the White House demands several procedural protections (or, depending on perspective, privileges) including the ability to subpoena its own witnesses and evidence. In the Nixon and Clinton cases, the House did grant subpoena power to the minority party, subject to override by majority vote of the investigating committee.

Second, the White House likely aims to force vulnerable Democrats in closely contested districts to vote either for an impeachment inquiry (and risk alienating voters opposed to impeachment) or against it (and risk alienating base Democratic voters and independents who favor impeachment).

Pelosi has signaled little interest in holding a formal vote. This is a calculated risk. On one hand, if the House does vote and approves the inquiry, Pelosi eliminates one of the White House's primary legal objections to House subpoenas. (There is little risk of Pelosi holding a vote and losing; as Speaker, she almost certainly would only take that step if she knew she had enough votes to carry the motion). On the other hand, a formal vote could enable Republicans to extract concessions including the subpoena power, as in the Nixon and Clinton impeachment proceedings.

Even if the House does vote to open a formal inquiry, do not expect the White House to suddenly start complying with House subpoenas. Nowhere in its letter does the White House so promise. And given the White House's well-established pattern of obstructionism, I'd expect it simply to turn to another basis to fight House subpoenas -- executive privilege or absolute immunity , for example. So, while a full House vote would defeat one of the White House's primary objections, Congressional investigators still would have to overcome other obstacles to obtain evidence from the Executive Branch.

Gary (New York): Who serves as the prosecutor in a Senate impeachment trial?

If the House impeaches President Trump, then it will appoint a team of House "managers " to present the case for impeachment in the Senate trial. During the 1999 Senate impeachment trial of Bill Clinton, the Republican-controlled House appointed a team of 13 representatives to serve as managers and present the case against Clinton. I'd expect the current House to include former prosecutors Adam Schiff Ted Lieu and Eric Swalwell, among others, on its team.

The President would appoint a team of lawyers to defend him. Those lawyers can come from anywhere, including private practice. Clinton chose a team of high-powered attorneys -- including White House counsel and private lawyers.

The 100 Senators then serve essentially as a jury, with a ⅔ vote -- 67 votes out of 100 -- required to convict and remove the subject from office.

Dave (Virginia): What is Trump's culpability for the cover-up (moving documents to a separate server) if he did not know or direct that to happen? Would the parties that did move the records have potential criminal liability?

If Trump did not know about or direct the movement of records of the July 25 Ukraine phone call to a separate electronic system, then he is not criminally liable. Even if an illegal action is taken to benefit or protect a particular person, that person cannot be charged unless he participated in the conduct in some way.

Anybody who did participate in the movement of records to the separate system could face liability for obstruction of justice or evidence tampering , but it would depend on the person's knowledge and intent. If, for example, an administrative assistant was instructed to physically move the records, but knew nothing about what the documents were or why they were being moved, that person would not be criminally liable. But if a White House staffer ordered the movement of the records intending to hide them from investigators or even from a potential future investigation, then criminal charges could well apply.

According to a senior White House official , the direction to move the transcripts came from National Security Council attorneys who "directed that the classified document be handled appropriately." White House officials also say that because the transcript was classified, there was nothing wrong with moving it to another system.

Anne (California): Can William Barr be forced to recuse himself from the Ukraine case?

The Attorney General absolutely should have recused himself from the Ukraine case, but he cannot be forced to do so.

Barr is now a witness in the case. Trump repeatedly mentioned Barr during the July 25 phone call with Zelensky. "[W]hatever you can do with the attorney general would be great," Trump tells Zelensky in one passage.

We do not yet know whether Barr actually did the things Trump said he would do, and the Justice Department has claimed Trump never contacted Barr about working with the Ukrainians. The Justice Department also denied that Barr had any contact with the Ukrainians.

Either way, Barr now has questions to answer. Did Trump or anyone else ever ask Barr to contact Ukraine? Did Barr know about communications between Trump or Rudy Giuliani and Ukraine? Like it or not, he is now a witness, and he has Trump's own words to thank for that.

One of the most fundamental rules of legal ethics is that a person cannot be both attorney and witness in the same case. That is especially true for Justice Department attorneys, who hold extraordinary power to bring criminal actions. Barr's own potential involvement as a witness in the case, at a minimum, creates an appearance of impropriety that he could and should have avoided by recusing.

All that said, while Barr plainly should have recused himself, there is simply no mechanism in the law to force him to do so. That is a decision left up to Barr himself, and he has botched it.

Becky (Texas): The Justice Department declined to investigate Trump's dealings with Ukraine because they determined that campaign dirt is not a "thing of value." Do you agree with this conclusion?

No, I think the Justice Department got it wrong here, and -- given Barr's history of slanting matters to favor Trump -- perhaps intentionally.

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It is a federal crime to solicit from a foreign national a "contribution or donation of money or other thing of value" connected to a campaign. As CNN has reported , Barr's Justice Department decided not to even open an investigation into the Ukraine matter because, in its reading, political dirt on a campaign opponent is not a "thing of value." That's a tortured reading so I suspect it raises questions about the Justice Department's true motives.

The Federal Election Commission has recognized the " broad scope " of the foreign-national prohibition and said that "even where the value of a good or service 'may be nominal or difficult to ascertain,'" such contributions can be illegal. It really boils down to common sense: If dirt on an electoral opponent has no value, then why do campaigns routinely spend tens of thousands of dollars (or more) on opposition research?

Three questions to watch:

1. What will we learn from the second whistleblower , and will more public servants come forward with information damaging to Trump?

2. How will the House respond to the Trump administration blocking the testimony of EU ambassador Gordon Sondland , who participated in a damning text chain discussing Trump's dealings with Ukraine?