House Democrats have upped the ante in the impeachment inquiry. President Donald Trump's efforts to make security assistance to Ukraine contingent on politically useful probes, they suggest, are a violation of criminal bribery law.

"The bribe is to grant or withhold military assistance in return for a public statement of a fake investigation into the elections," said House Speaker Rep. Nancy Pelosi (D–Calif.) at a press conference on Thursday. "That's bribery."

Weighing in on Neil Cavuto's Fox News program, Judge Andrew Napolitano explained that "it wouldn't matter if it was Joe Biden or Joe Blow" who was at the center of the investigations sought by Trump. It's also inconsequential, he said, "whether the favor comes or not." (Republicans have argued that, since the aid was released before the country conducted any investigations, there was no quo in the quid pro quo. Others counter that this only happened because Congress started getting suspicious.)

"I think that the argument that asking for a favor in return for doing a legal obligation—releasing the [security] funds—is pretty clearly a violation of criminal bribery laws," Napolitano told Cavuto. "Republicans may not want to acknowledge that, which is why they'd rather undermine the witnesses than address the merits."

Napolitano is referring to the first day of impeachment inquiry testimony, when the two witnesses—William B. Taylor, the chargé d'affaires in Ukraine, and George Kent, the deputy assistant secretary of state for European and Eurasian affairs—railed against Trump's attempts to push Ukraine into investigating a political rival. In response, the minority party characterized both men as liable to have misrepresented or misunderstood interactions they had with those close in Trump's circle.

According to Rep. Justin Amash (I–Mich.), the libertarian-minded congressman who left the Republican Party in July, there is an easy way to gain clarity.

"This is simple. Keep it simple," he tweeted on Wednesday. "The White House released security assistance to Ukraine only after Congress started asking questions. Why? Considering that Bolton, Giuliani, Mulvaney, and others may have pertinent first-hand testimony, why won't President Trump let them testify?"