Valerie Biden Owens, ADPH

Valerie Biden Owens, former Vice President Joe Biden's sister and longtime adviser, pictured here during a campaign stop in Aiken Monday.

President Donald Trump's aggression toward Joe Biden, including overt suggestions made to China and Ukraine to probe him and his family, is a public display of Trump's intimidation as the former vice president's campaign surges, Valerie Biden Owens said Monday.

Biden Owens, the presidential candidate's sister and longtime political adviser, spoke to the Aiken Standard after a campaign event. She further described Trump as a bully and her brother as the person he's "afraid of."

"Why? Why Joe? Because he's darn good, and he'd make a spectacular president," said Biden Owens, who also said the current president is using the Biden name as a means to an end.

"And to take out an opponent, your rival, with foreign intervention, which he called for before in the last election, and it's there, is horrific," she said, referencing Russian interference in the 2016 election.

Valerie Biden Owens, Stump Speech, Aiken

Valerie Biden Owens speaks to a crowd gathered at the Aiken County Democratic Party's Richland Avenue headquarters on Monday. About 20 people showed up for the event.

The 47th vice president – who announced his presidential campaign later than most other candidates – is the clear-cut Democratic favorite in South Carolina, according to a recent Winthrop University poll.

About 37% of the Palmetto State's Democratic or Democratic-leaning voters surveyed favored Biden, ahead of U.S. Sens. Elizabeth Warren of Massachusetts (17%), Bernie Sanders of Vermont (8%) and Kamala Harris of California (7%). The poll had a relevant margin of error of plus or minus 4.6%.

"South Carolina Democratic voters strongly support Joe Biden to be the Democratic nominee to become the 46th president, according to the latest Winthrop Poll," reads an Oct. 1 introduction to the findings.

"So we really do have something going," Biden Owens said Monday. She's been described as Biden's principal surrogate on the campaign trail.

Trump earlier this month, answering questions from reporters outside the White House, said Ukraine "should investigate the Bidens," a nod to his July conversation with Ukrainian President Volodymyr Zelensky, the subject of much scrutiny.

"And by the way, likewise, China should start an investigation into the Bidens," the president continued. "Because what happened in China is just about as bad as what happened with Ukraine."

Biden Owens said Monday what it boils down to is an abuse of power.

"Abuse of power is the defining characteristic of the Trump presidency," Biden wrote on Twitter on Oct. 7. "Donald Trump has abused the foreign policy of the United States to extract personal, political favors from multiple countries. We must stop him."

Similar arguments have been made by congressional Democrats, who have launched a formal impeachment inquiry into the president.

Biden Owens – who alluded to Trump being "untruthful, unstable and erratic" – said the inquiry is warranted.

"And I think you have to follow the law. Like, what a strange concept," she said. "You follow the law, and you see what's there."

Colin Demarest covers the Savannah River Site, the U.S. Department of Energy, the National Nuclear Security Administration and government in general. Follow him on Twitter: @demarest_colin