WASHINGTON – The Ukraine scandal enveloping President Donald Trump's administration could provide the biggest test yet for one of his most loyal soldiers.

Vice President Mike Pence's name has surfaced in the appendix of the explosive whistleblower report released this week. And Trump pointed out Wednesday that Pence had his own interactions with Ukraine's leaders.

As the Democratic impeachment inquiry focused on Urkaine moves forward, Pence could be pressed to disclose what he knows about the Trump's dealings with Ukrainian President Volodymyr Zelensky and the effort to push Zelensky to investigate former Vice President Joe Biden.

House Speaker Nancy Pelosi said Trump's actions show he betrayed his oath of office, the nation's security and the integrity of elections.

White House officials deny that Trump pressured Ukraine to do anything and note that the whistleblower said he did not witness most of the events described in the nine-page report.

Here’s how Pence has been brought into the debate:

Whistleblower complaint

Pence is mentioned once in the declassified version of the whistleblower complaint, in an appendix giving more information about the events leading up to Trump’s July call with Zelensky.

In mid-May, the whistleblower learned from U.S. officials, Trump instructed Pence to cancel his plans to attend Zelensky’s May 20 inauguration. Energy Secretary Rick Perry went instead.

That detail was given in the context of officials telling the whistleblower that it had been “made clear” to them that Trump didn’t want to meet with Zelensky until he saw how the new leader “chose to act” in office.

Trump mentions Pence

After the White House released Wednesday a summary of the July call, Trump said the summary exonerated him and reporters should also review an earlier call with Zelensky as well as Pence’s communications with the Ukrainian president.

“I think you should do that,” he said during a news conference at the United Nations. “And I think you should ask for VP Pence’s conversation because he had a couple conversations also.”

Trump said nothing of import was mentioned in the calls other than congratulations to the newly-elected Zelensky.

“They were perfect,” Trump said of the calls. “They were all perfect.”

But Trump’s remarks prompted some commentators to wonder if the president was trying to tar one of his most loyal defenders with the developing scandal.

“Why is Trump throwing Pence under the bus? Trying to keep him quiet?” tweeted Jennifer Rubin, a conservative columnist for The Washington Post and a critic of both Trump and Pence.

Democrat Ron Klain, who worked for Biden and former Vice President Al Gore, brought up a popular game theory example showing how two people might not cooperate, even if it’s in their best interests to do so. The participants may think they’re protecting themselves at the expense of the other person, but instead find themselves worse off.

“If you had 'fail’ in your office pool on how Trump would play the prisoner’s dilemma game with Pence, you were correct,” Klain tweeted.

Pence met with Zelensky

When Pence substituted for Trump at the last minute on a trip to Poland this month, he had a private meeting with Zelensky. During a news conference the next day, Pence was asked whether he discussed Biden with Zelensky.

“The answer is no,” Pence said.

He gave a less direct response to the question of whether he could assure Ukraine that a hold up of military assistance was not related to efforts by Trump allies to try to dig up dirt on Biden.

Pence said Trump had asked him to talk to Zelensky “about the progress that he’s making on a broad range of areas.” That included, Pence said, steps Zelensky has taken to address public corruption and restore integrity to the public process.

“As President Trump had me make clear, we have great concerns about issues of corruption,” Pence said as part of his lengthy answer.

Viola Gienger, a research scholar at the New York University School of Law, found Pence’s response interesting.

“He essentially demurred,” Gienger wrote in an essay for JustSecurity.org, an online forum for analysis of U.S. national security law and policy.

Pence’s recent responses

Pence hasn’t publicly commented on his inclusion in the whistleblower’s report.

He ignored reporters' shouted questions to him about the report as he deplaned in Indianapolis Thursday morning for a two-day visit to his home state.

Appearing on the Fox Business Network Wednesday night, Pence told host Lou Dobbs that Trump had spoken with Zelensky “about issues that were appropriate.”

“The president was concerned about corruption,” Pence said. “And seeing this new leader rise – in President Zelensky on a message of anti-corruption, the president raised that issue, they both spoke about it.”

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Pence’s past views on foreign involvement

As Pence defended Trump’s conduct this week, critics circulated a clip from the 2016 vice presidential debate showing Pence taking a tougher line on foreign involvement in U.S. elections. Pence called it improper for the Clinton Foundation to have accepted tens of millions of dollars from foreign governments and foreign donors while she was secretary of state.

“Foreign governments cannot participate in the American political process,” candidate Pence said then.

In Trump's case, multiple government officials relayed to the whistleblower that the president "is using the power of his office to solicit interference from a foreign country in the 2020 U.S. election," according to the complaint.

Pence and the Mueller investigation

Pence was on the periphery of the special counsel investigation into the Trump campaign and Russia's efforts to interfere in the 2016 election. His exposure was primarily through statements he'd made that were later contradicted.

Pence was not asked by Mueller's team for an interview but provided documents, racking up about $500,000 in legal bills in the process.

House Democrats have been following up on aspects of Mueller's report. But Pelosi emphasized Thursday that the impeachment inquiry she announced Tuesday is focused – at least for now – on Trump's action regarding Ukraine.

Impeachment inquiry timeline:A diagram of events in the impeachment inquiry of President Trump

What’s next?

Congressional Democrats have not gone after Pence so far. But he's likely to face questions about his interactions with Zelensky.

If both the president and vice president are removed from office, the House chooses the next president. Some noted Wednesday that “President Pelosi” was trending on Twitter.

If the House were to impeach Trump, Democrats would then have to persuade at least 20 Senate Republicans to vote for his conviction for Trump to be removed from office.

Some conservative commentators are wondering if Republican lawmakers will turn on Trump and turn to Pence for self-preservation.

“Why wouldn’t (Sens. Ben) Sasse, (Mitt) Romney and others invite Pence in for a chat?” Rubin tweeted. “Trump has to go. Pence can be president for 18 mos and agree not to run for re-election (he’d lose anyway). All of them can run for POTUS instead.”

Erick Erickson, a conservative blogger and radio talk show hosts, tweeted that Republicans have put up with a lot but senators may reach a breaking point “and just decide they’ll take their chances with President Pence and an angry base they won’t have to face till 2022 or later.”

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