The intelligence community’s top watchdog is huddling Friday with House Intelligence Committee members of both parties, a day after the release of explosive text messages between leading administration officials that have fueled the Democrats' impeachment inquiry into President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE.

Michael Atkinson, inspector general (IG) of the intelligence community, had previously expressed grave concerns over a whistleblower complaint alleging that Trump had threatened to withhold U.S. military aid to Ukraine unless that country's president launched an investigation into one of Trump's top political rivals, former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE.

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Federal election law bars campaigns from receiving gifts from foreign entities. And Democrats' impeachment inquiry, now being led by Intelligence Committee Chairman Adam Schiff Adam Bennett SchiffSchiff to subpoena top DHS official, alleges whistleblower deposition is being stonewalled Schiff claims DHS is blocking whistleblower's access to records before testimony GOP lawmakers distance themselves from Trump comments on transfer of power MORE (D-Calif.), is focused on whether Trump abused his power by asking a foreign leader to interfere in the 2020 election to give him a boost.

Atkinson has deemed the whistleblower complaint of "urgent concern," largely for its implications for election security. And he is said to have already interviewed multiple witnesses with knowledge of Trump's July 25 call with Ukrainian President Volodymyr Zelensky.

Against that backdrop, Atkinson's testimony carries high stakes for both parties. And as the IG entered the Capitol basement just before 10 a.m. Friday, rows of cameras and scores of reporters were lined up in hallways that would otherwise have been empty amid the long congressional recess.

The IG offered no comment as he came in.

Lawmakers on the Intelligence Committee began trickling in afterwards, including GOP Reps. Devin Nunes Devin Gerald NunesOvernight Defense: Stopgap spending measure awaits Senate vote | Trump nominates former Nunes aide for intelligence community watchdog | Trump extends ban on racial discrimination training to contractors, military Trump nominates former Nunes aide to serve as intel community inspector general Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election MORE (Calif.), the panel's ranking member, and Mike Conaway Kenneth (Mike) Michael ConawayBottom line House Republican introduces amendment to include farm aid in stopgap funding bill Live coverage: Democrats, Republicans seek to win PR battle in final House impeachment hearing MORE (Texas), as well as Democratic Reps. Jim Himes James (Jim) Andres HimesMany Democrats want John Bolton's testimony, but Pelosi stays mum SEC's Clayton demurs on firing of Manhattan US attorney he would replace Democrats face tough questions with Bolton MORE (Conn.) Eric Swalwell Eric Michael SwalwellHouse to vote on resolution affirming peaceful transition of power Swalwell calls for creation of presidential crimes commission to investigate Trump when he leaves office 'This already exists': Democrats seize on potential Trump executive order on preexisting conditions MORE (Calif.) and Peter Welch Peter Francis WelchShakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' Vermont Rep. Peter Welch easily wins primary Vermont has a chance to show how bipartisanship can tackle systemic racism MORE (Vt.).

Atkinson's testimony comes a day after three House committees — Intelligence, Oversight and Reform and Foreign Affairs — deposed another key figure in the whistleblower complaint: Kurt Volker Kurt VolkerGOP senators request details on Hunter Biden's travel for probe Yovanovitch retires from State Department: reports Live coverage: Senators enter second day of questions in impeachment trial MORE, who was Trump's envoy to Ukraine for more than two years before resigning that post last week amid the whistleblower furor.

After roughly nine hours behind closed doors, lawmakers from both parties said Volker's testimony had only bolstered their conflicting cases — highlighting the entrenched partisanship surrounding the Democrats' impeachment inquiry into the president.

Hours later, Democratic leaders released transcripts of communications among Volker, Trump's personal attorney Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE and two other top diplomats that appear to reveal a coordinated effort to pressure Zelensky to commit to an investigation into Biden and his son, Hunter Biden, who was employed by a Ukrainian energy company while Joe Biden was vice president.

One of those diplomats, William Taylor, the U.S. chargé d'affaires in Ukraine, expressed concerns last month that Trump was crossing a line by dangling military aid to pressure Zelensky for political favors.

"I think it's crazy to withhold security assistance for help with a political campaign," Taylor wrote to Gordon Sondland, the U.S. ambassador to the European Union, on Sept. 9.

Sondland rejected that characterization, saying Trump "has been crystal clear no quid pro quo's of any kind."

"The President is trying to evaluate whether Ukraine is truly going to adopt the transparency and reforms that President Zelenskiy promised during his campaign," Sondland wrote, adding that they should “stop the back and forth by text.”

That argument has does little to assuage the concerns of Democrats, who are pressing forward aggressively with their impeachment inquiry amid growing pressure from the left to draft articles and bring them to the floor.

“This is not normal or acceptable. It is unethical, unpatriotic, and wrong," Schiff, Oversight Chairman Elijah Cummings Elijah Eugene CummingsBlack GOP candidate accuses Behar of wearing black face in heated interview Overnight Health Care: US won't join global coronavirus vaccine initiative | Federal panel lays out initial priorities for COVID-19 vaccine distribution | NIH panel: 'Insufficient data' to show treatment touted by Trump works House Oversight Democrats to subpoena AbbVie in drug pricing probe MORE (D-Md.), and Foreign Affairs Chairman Eliot Engel Eliot Lance EngelHouse panel halts contempt proceedings against Pompeo after documents turned over Engel subpoenas US global media chief Michael Pack The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep MORE (D-N.Y.) wrote to their Democratic colleagues late Thursday night.

"American Presidents should never press foreign powers to target their domestic political rivals."