Former GOP Rep. Carlos Curbelo Carlos Luis CurbeloGOP wants more vision, policy from Trump at convention Mucarsel-Powell, Giménez to battle for Florida swing district The Memo: GOP cringes at new Trump race controversy MORE (Fla.) on Thursday demanded that Republicans in Congress "unequivocally" condemn Trump's call for Ukraine and China to investigate 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 and his son.

"This is unacceptable," Curbelo, a moderate Republican who lost his reelection bid during last year's midterm elections, said on Twitter. "Republicans must condemn it unequivocally. Time is running out for them to get on the right side of history. Our institutions and being diminished in a very dangerous way."

This is unacceptable. Republicans must condemn it unequivocally. Time is running out for them to get on the right side of history. Our institutions and being diminished in a very dangerous way. https://t.co/M0gW5nD0yA — Carlos Curbelo (@carloslcurbelo) October 3, 2019

"It’s high time for people to honor our country and its Constitution," he added in a subsequent tweet. "A lot of Republicans are watching from the sidelines. Get in the game and tell the American people what you really think."

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While speaking with reporters Thursday, Trump stepped up his efforts to put Biden under scrutiny , calling on both Ukraine and China to open investigations into matters related to the 2020 presidential candidate and his son, Hunter Biden.

The comments came as Trump is facing heat over a whistleblower complaint that accuses him of enlisting Ukraine's help in his 2020 reelection efforts. Revelations regarding Trump's interactions with Ukrainian President Volodymyr Zelensky prompted House Democrats to launch a formal impeachment inquiry.

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Trump said that Ukraine would start a "major investigation" into the Biden family if they were being "honest" about the situation.

“I would say that President Zelensky — if it were me, I would recommend they start an investigation into the Bidens,” Trump said after being asked about a July 25 phone call in which he pressured the Ukrainian leader to look into the Bidens over unsubstantiated allegations of corruption. "Because nobody doubts they weren't crooked."

“China should start an investigation into the Bidens,” Trump added.

The president noted that he hasn't explicitly asked Chinese President Xi Jinping to open an investigation. But he said it it is “certainly something we can start thinking about.”

Biden's campaign immediately issued a strong rebuke of the president's remarks, saying they represented "a grotesque choice of lies over truth and self over country."

Rep. Justin Amash Justin AmashRon Paul hospitalized in Texas Internal Democratic poll shows tight race in contest to replace Amash Centrist Democrats 'strongly considering' discharge petition on GOP PPP bill MORE (Mich.), an independent who formally left the Republican Party earlier this year, called Trump's statements an open challenge to "our system of checks and balances."

He’s openly challenging our system of checks and balances. In plain sight, he’s using the powers of his public office for personal gain and counting on Republicans in Congress to look the other way. https://t.co/dJo7B5CI1G — Justin Amash (@justinamash) October 3, 2019

"In plain sight, he’s using the powers of his public office for personal gain and counting on Republicans in Congress to look the other way," Amash, who has expressed support for impeachment, said on Twitter.

Details about the president's interactions with Ukraine led to a wave of Democrats, including Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.), coming out in support of opening an impeachment inquiry.

Meanwhile, many Republican lawmakers have come to the defense of Trump, arguing that the president's conversations with the Ukrainian leader were appropriate. Trump has defended his interactions as "perfect" while deriding the whistleblower's complaint as "fraudulent."