Washington(CNN) When President Donald Trump suggested — without prompting — that China should investigate Joe Biden and his son, he thrust another political grudge into what was already the world's most complicated and consequential relationship.

The move startled Chinese officials, who say they have little interest in becoming embroiled in a US political controversy. And it amounted to the latest extraordinary effort by Trump to openly request political assistance from foreign governments.

Thursday's comments weren't the first time Trump has injected Biden into his relationship with China, though he said Thursday he has never pushed Xi to investigate the former vice president. Nor is it the first time he has sought to trade favors with Xi, who this week celebrated the 70th birthday of his communist state with a note of congratulations from Trump.

During a phone call with Xi on June 18, Trump raised Biden's political prospects as well as those of Sen. Elizabeth Warren, who by then had started rising in the polls, according to two people familiar with the discussion. In that call, Trump also told Xi he would remain quiet on Hong Kong protests as trade talks progressed.

The White House record of that call was later stored in the highly secured electronic system used to house a now-infamous phone call with Ukraine's President and which helped spark a whistleblower complaint that's led Democrats to open an impeachment inquiry into Trump.

Asked earlier this week about Trump's call with Xi, the White House did not deny that he raised Biden.

"World leaders need to be able to speak freely in their conversations with the President--that is a key component to effective diplomacy. And that is why such conversations are kept confidential," said White House press secretary Stephanie Grisham. "We are not going to start discussing the contents of every conversation President Trump has with world leaders, other than to say his conversations are always appropriate."

After this story published, Warren reacted to news of Trump's call with Xi, writing on Twitter, "Trump can say what he wants about me, but it's outrageous that any president would sell out the people of Hong Kong behind closed doors. The public must see the transcript of Trump's call with Xi. And we need a leader who will stand up for our values."

On Thursday, Trump told reporters at the White House he'd consider asking his counterpart in Beijing to investigate the Bidens, adding to a growing list of foreign leaders he's tried to enlist in his attempts to bring down a potential Democratic challenger.

"It's certainly something we can start thinking about," Trump said when questioned whether he would seek the help of Xi in investigating Biden. "Because I'm sure that President Xi does not like being under that kind of scrutiny."

Scramble for clarity

Trump's comments sparked confusion and a scramble for explanation from Chinese officials.

"Are you asking about the comments that Trump just made? I don't think I can tell you anything in this regard right now," said one Chinese diplomat when questioned on Thursday about Trump's remarks.

"This is quite chaotic," the diplomat said. "We do not want to get in the middle of the US politics."

One Trump ally outside the White House described receiving a message from Chinese government officials asking if Trump was serious when he suggested China open an investigation into Biden. The response: investigating corruption is an easy way to earn goodwill with Trump.

The Chinese did not immediately clarify if they would be launching an investigation -- or if they would make it public if they do.

Looming trade talks

As trade negotiators prepare for another round of talks and as Xi contends with domestic challenges like the Hong Kong unrest, the Biden matter throws another wrench into tangled but high-stakes diplomacy.

Trump's reluctance over the summer to speak out against a crackdown against pro-Democracy protesters in Hong Kong has frustrated officials at the National Security Council and State Department, who had been advocating a firmer US stance.

While Trump eventually did tweet out a call for Xi to find a "humane" resolution to the Hong Kong unrest, he did not issue a forceful call to uphold human rights in the former British colony. And as protests again erupted this week as massive celebrations were underway in Beijing for the 70th anniversary of the People's Republic of China, Trump offered Xi his congratulations.

"Congratulations to President Xi and the Chinese people on the 70th Anniversary of the People's Republic of China!" Trump wrote, adopted a drastically different tone than his Republican allies, who used words like "ghoulish," "authoritarian" and "horrors" to mark the occasion.

Trump's remarks Thursday have caused consternation among some of his aides, who have privately pined for an end to a trade war that is starting to take a toll on the US economy.

Only minutes before suggesting China investigate Biden, Trump implied he held the upper hand with China in trade talks, which are set to pick up next week when China's chief negotiator comes to Washington.

"I have a lot of options on China," Trump said. "But if they don't do what we want, we have tremendous power."

Already, some of the President's trade advisers say they believe China is watching the Democratic primary closely, making calculations on whether to agree to a new deal with Trump based on the prospects of various candidates.

Biden allegations

On several occasions, Trump has intimated that the Bidens have received millions of dollars from China, implying they capitalized on the then-vice president's political power and connections.

The allegations stem partly from an official trip both Bidens took to China in 2013, meant as a diplomatic mission to help ease tensions in the region. A company on whose board Hunter Biden sat received a large investment of Chinese capital shortly after the trip.

According to the New York Times, Hunter has a 10% interest in BHR Partners, a private-equity fund that the Chinese government-owned Bank of China has invested in. As of May 2019, both The New York Times and the Washington Post reported that Hunter had not received any money from the fund or in connection with his role as an unpaid advisory board member.

In July 2019, more than two years after his father left office, Hunter purchased an equity stake in the BHR fund, valued around $430,000, according to the Washington Post.

There is no evidence the former vice president received money from China, and last week one of Hunter Biden's lawyers told the Washington Post that he hadn't received any "return or compensation on account of this investment or his position on the board of directors."

Hunter Biden's lawyer has also said he did not conduct any business related to the investment fund during the 2013 trip, on which he was accompanied by one of his daughters.

In a statement after Trump's comments on Thursday, Biden's deputy campaign manager Kate Bedingfield called his comments "a grotesque choice of lies over truth and self over the country."

Biden's successor, however, made clear he saw nothing wrong with Trump's behavior.

"The President made it very clear that he believes our other nations around the world should look into it as well," Vice President Mike Pence said during an appearance in Arizona, where he was working to sell a new North American trade deal.

"The simple fact is that, you know, when you hold the second highest office in the land, it comes with unique responsibilities. Not just to be above impropriety but to be above the appearance of impropriety," Pence said.

Privately, Trump has been telling allies over the past week he believes Hunter Biden's activities in China to be potentially more damaging than his business in Ukraine.

"That's not the best one. The best one was China," Trump said at a private event in New York last week after going on a screed about the unfounded claims involving the Bidens and Ukraine.

Trump's insistence that Hunter Biden profited off his father's political position is not without irony. Beijing granted approval for fashion and accessory trademarks to Trump's daughter Ivanka last year, even after she shuttered her eponymous brand in July 2018 because of slow sales.

The President's attempts to build a relationship with Xi have proceeded in fits and starts since taking office. He was feted with a grand state visit during his first year in office, sipping tea with Xi inside the Forbidden City. He later reciprocated by hosting Xi at Mar-a-Lago.

But he's not the only player in the impeachment saga with close ties to Xi. Biden was tasked during the Obama administration with courting then-Vice President Xi during his apprenticeship for China's top job. They traveled together both in the US and China.

"I've spent as much time with Xi Jinping as anybody has," Biden has boasted on campaign trail, hoping to burnish his foreign policy credentials.

The story has been updated with comment from the White House and Elizabeth Warren.