President Trump is pushing the limits on how much Congress will tolerate of a president using his office to target political rivals.

Why it matters: Ukraine is reportedly at the center of a whistleblower's concerns over Trump's contact with a foreign leader, the WashPost and N.Y. Times report.

The phone call: Trump reportedly urged Ukrainian President Volodymyr Zelensky "about eight times" to cooperate with his personal lawyer Rudy Giuliani on investigating Joe Biden's son Hunter, the WSJ reported Friday afternoon.

Trump reportedly urged Ukrainian President Volodymyr Zelensky "about eight times" to cooperate with his personal lawyer Rudy Giuliani on investigating Joe Biden's son Hunter, the WSJ reported Friday afternoon. The whistleblower: While few specifics are known about the whistleblower complaint, Trump's call with Zelensky was two weeks before the issue was raised. Per the Post, Trump made a "promise" that troubled a member of the intelligence community.

While few specifics are known about the whistleblower complaint, Trump's call with Zelensky was two weeks before the issue was raised. Per the Post, Trump made a "promise" that troubled a member of the intelligence community. The standoff: Acting Director of National Intelligence Joseph Maguire and the Justice Department have blocked Congress from accessing that whistleblower report, despite an intelligence community watchdog's referral.

Acting Director of National Intelligence Joseph Maguire and the Justice Department have blocked Congress from accessing that whistleblower report, despite an intelligence community watchdog's referral. The pressure: “Of course I did," Giuliani told CNN last night, when asked if he's pressured Ukraine on investigating Biden. Giuliani later tweeted that a "President telling a Pres-elect of a well known corrupt country he better investigate corruption that affects US is doing his job."

“Of course I did," Giuliani told CNN last night, when asked if he's pressured Ukraine on investigating Biden. Giuliani later tweeted that a "President telling a Pres-elect of a well known corrupt country he better investigate corruption that affects US is doing his job." The money: The Trump administration has been withholding $250 million in aid for Ukraine that's meant to deter Russia. In July, Trump told Zelensky that the key to improving ties was Ukraine investigating corruption.

Between the lines: It's not clear that this example provides a reasonable case for investigation into the Biden family, as JustSecurity noted earlier this month.

"Trump and Giuliani allege , contrary to evidence, that Biden improperly pressured the Ukrainian government in 2016 to fire then-Prosecutor General Viktor Shokin in the midst of a corruption investigation of one of Ukraine’s biggest gas companies, Burisma Group. Biden’s youngest son, Hunter, was serving on the company’s board at the time."

, contrary to evidence, that Biden improperly pressured the Ukrainian government in 2016 to fire then-Prosecutor General Viktor Shokin in the midst of a corruption investigation of one of Ukraine’s biggest gas companies, Burisma Group. Biden’s youngest son, Hunter, was serving on the company’s board at the time." "But the prosecutor ... was the target of pressure by Ukrainian anti-corruption advocates and a host of international supporters of Ukraine, who argued he should be fired for failing to pursue major cases of corruption."

was the target of pressure by Ukrainian anti-corruption advocates and a host of international supporters of Ukraine, who argued he should be fired for failing to pursue major cases of corruption." "And it was the widely known and publicly espoused position of the U.S. government ... that the prosecutor’s ouster was among crucial anti-corruption measures that the Ukrainian government needed to take."

and publicly espoused position of the U.S. government ... that the prosecutor’s ouster was among crucial anti-corruption measures that the Ukrainian government needed to take." The other side: "Several former officials in the Obama Administration ... insisted that Hunter’s role at Burisma had no effect on his father’s policies in Ukraine, but said that, nevertheless, Hunter should not have taken the board seat," The New Yorker reported earlier this year.

What's next: Zelensky is among the world leaders with whom Trump is slated to meet next week at the UN General Assembly.

Expect Democrats to keep pushing for more information on the whistleblower report, as well as for more details on Trump's phone calls.

for more information on the whistleblower report, as well as for more details on Trump's phone calls. "If it's true that the president requested that the president of Ukraine interfere in an American election, we are in really dangerous, brand new territory," Sen. Chris Murphy (D-Conn.) told the WashPost's Bob Costa today.

The bottom line: “It doesn’t matter what I discussed but I will say this, somebody ought to look into Joe Biden," Trump told reporters Friday.