"You won't destroy me, and you won't destroy my family," U.S. Democratic presidential candidate and former Vice President Joe Biden wrote in an opinion piece for The Washington Post on Saturday, his latest response to President Donald Trump's call for an investigation into him and his son.

Trump's request for an investigation into the Bidens, directed to Ukrainian President Volodymyr Zelensky in a July 25 phone call, has prompted an increasingly escalating impeachment inquiry initiated by House Democrats.

This combination of pictures created on September 24, 2019 shows a file photo taken on September 12, 2019 of Democratic presidential hopeful Former Vice President Joe Biden at Texas Southern University in Houston, Texas,and US President Donald Trump during a meeting in the Oval Office at the White House in Washington, DC, September 20, 2019. [Photo: VCG]

In the article, Biden said Trump seeking help from foreign countries in order to "extract political favors" was an "abuse of power," which he claimed "is the defining characteristic of the Trump presidency."

"President Trump is abusing the power of the presidency and is wholly unfit to be president," Biden wrote in direct attack on his 2020 election rival. "He is using the highest office in the land to advance his personal political interests instead of the national interest."

A whistleblower complaint filed in late August by an unidentified intelligence official alleged that Trump asked Zelensly during the call to probe Biden and his son Hunter Biden, who once worked for Ukrainian gas company Burisma Holdings that was accused of corruption. There has so far been no evidence of wrongdoing by either Biden senior or junior.

However, the former vice president, during an event in January 2018 at the Council on Foreign Relations, bragged about how he in 2016 successfully persuaded the Ukrainian authorities to sack the country's then prosecutor general, Viktor Shokin, who was investigating Burisma Holdings at the time.

Trump claimed that his intent to scrutinize the Bidens was out of concerns over corruption, not politically motivated or aimed at sabotaging Biden's presidential campaign.

"As President I have an obligation to end CORRUPTION, even if that means requesting the help of a foreign country or countries," the president tweeted Friday. "This has NOTHING to do with politics or a political campaign against the Bidens. This does have to do with their corruption!"

Biden, for his part, vowed in a combative tone at the end of his article: "And come November 2020, I intend to beat you like a drum."