Several sought clarity on answers delivered a day earlier, including arguments from White House lawyers that foreign involvement in an election isn't automatically inappropriate and that presidents acting in what they think is the national interest enjoy broad latitude in what they do.
A look at some of the more notable exchanges:
SEN. SHERROD BROWN, D
OHIO, and SEN. RON WYDEN, D-ORE: “If President Trump remains in office, what signal does that send to other countries intent on interfering with our election s in the future and what might we expect from those countries and the president?"
— The question came in response to an argument a night earlier from deputy White House counsel Patrick Philbin, who said foreign involvement in an election isn't by itself improper if it's simply bringing to light credible information about a candidate for office.
Those comments instantly angered Democrats, and Thursday's question from the senators pointedly noted that FBI Director Chris Wray has said anyone with information about foreign election interference should immediately contact law enforcement.
Rep. Hakeem Jeffries, a New York Democrat and House impeachment manager, said he was shocked by Philbin's suggestion that there could be scenarios in which it was acceptable to receive dirt on an opponent from a foreign national.
“This is not a banana republic. It's the democratic republic of the United States of America. It's wrong," Jeffries said.
— The question is part of a long-running effort by Republicans to paint the impeachment as a partisan effort to oust the president rather than a fact-finding mission.
It provoked an animated — sometimes snide — defense of the president from Trump attorney Eric Herschmann, who rattled off a series of what he said were the administration's accomplishments, including the killing by the U.S. military last fall of Islamic State founder Abu Bakr al-Baghdadi.
“If all that is solely — solely, in their words — for his personal and political gain and not in the best interest of the American people, then I say, God bless him," Herschmann said. “Keep doing it. Keep doing it. Keep doing it.”
If House managers stop “harassing" Trump and his aides with letters and investigations, Herschmann added, then “maybe we can get even more done."
SEN. SUSAN COLLINS, R-MAINE, SEN. MARCO RUBIO, R-FLA., SEN. MIKE CRAPO, R-IDAHO, and SEN. ROY BLUNT, R-MO.: “Are there legitimate circumstances under which a president could request a foreign country to investigate a U.S. citizen, including a political rival, who is not under investigation by the U.S. government? If so, what are they and how do they apply to the present case?”
— Any question from Collins is important because she is among the Republicans whose perspective on both witnesses and acquittal is being closely watched for clues.
In this question, she appears to be grappling with whether there are instances in which conduct similar to that at issue in the impeachment case — Trump asked Ukraine's leader last summer to investigate Democratic rival Joe Biden and his son — might be reasonable.
Rep. Adam Schiff, the lead House impeachment prosecutor, said he could not imagine such a circumstance. The president, Schiff said, has “affirmatively and aggressively sought to investigate his rivals."
Philbin contended that Trump didn't specifically ask Ukrainian President Volodymyr Zelenskiy for a general investigation into the Bidens, but instead to look into the firing of a Ukraine prosecutor that took place at the same time that Hunter Biden served on the board of a Ukraine gas company.
He said it could be “perfectly legitimate" to seek an investigation overseas into someone suspected of violating the laws of that country.
SEN. KRYSTEN SINEMA, D-ARIZ., SEN. JOE MANCHIN, D-W.VA., SEN. LISA MURKOWSKI, R-ARK., SEN. SUSAN COLLINS, R-MAINE: “Will the president assure the American public that private citizens will not be directed to conduct American foreign policy or national security policy unless they have been specifically and formally designated by the president and the State Department to do so?”
— The lead-up to the question referenced the Logan Act, an obscure and virtually dormant law that prohibits private citizens from negotiating without authorization with foreign powers.
The question — posed by senators of both parties — also made an oblique but unmistakable reference to Rudy Giuliani, the president’s personal lawyer and a central figure in the impeachment saga for his efforts to press Ukraine for the investigations the president wanted and for the ouster of the U.S. ambassador to Ukraine.
Philbin took exception to the question, saying there was “no conduct of foreign policy being carried on here by a private person.”
Giuliani’s outreach to Ukraine was not formal foreign policy, Philbin argued. And in any event, he said, presidents since George Washington have relied on confidants and others outside their administration to carry messages to other countries and to function as a go-between.
Associated Press writer Lisa Mascaro contributed to this report.