Former Vice President Joe Biden on Wednesday pointedly refused to rule out a presidential run in 2020, telling an audience in London only that he has no plans "at this point" to take his war of words with President Trump to the voters.

"I think there are many people in the Democratic Party that can defeat Trump and not a single aspiring candidate that I can think of for the nomination -- and I am not one at this point -- does not have a better understanding and formulation of American foreign policy than President Trump," Biden said at the Royal Institute of International Affairs, a think tank commonly known as Chatham House.

He continued: "I'm not being rankly partisan here -- the president acknowledged at the outset he didn't know a lot about foreign policy. ... I think there are any number of potential candidates seeking the nomination, from [Sen.] Kamala Harris [D-Calif.] to a whole range of people in my party, who would pursue a much more enlightened foreign policy than the president."

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The 75-year-old Biden, who would be the oldest living president at 79 if he took office in January 2021, has been unrelenting critic of the Trump administration. Earlier this year, Biden vowed that he would have "beat[en] the hell out of" Trump in high school because of the Republican's boasts about women in the leaked "Access Hollywood" tape.

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This summer, Biden panned the family separations resulting from the White House's "zero-tolerance" policy on illegal immigrants as "one of the darkest moments in our history." And in September, Biden openly mocked Trump's claims about his own intelligence.

For his part, Trump -- who often uses his campaign-style rallies to test-fire new broadsides against potential 2020 rivals -- has hit back at Biden's physical and mental prowess, saying it would be no trouble at all to rough up the former vice president.

“Remember, he challenged me to a fight," Trump said last week at a rally in Kansas. "'I’d like to take him behind the barn.’ I’d love that. That wouldn’t last long. That would not last long. That wouldn’t last long,” Trump told the crowd. Then, after imitating a punch, he continued: "He's down, and he'll never get up."

Trump has also variously called Biden "crazy" and "sleepy," referring to videos apparently showing Biden falling asleep during speeches.

Owing to what he said was rising anti-Trump sentiment, the former vice president on Wednesday was bullish on Democrats' chances in the upcoming midterm elections in November. He predicted that progressive candidates could realistically take back not only the House, but also the Senate -- where the 35 seats up for election are in GOP-leaning states.

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"I predict to you the Democrats will win 40 seats in the House. And I predict to you there's a slightly better than even chance we win the Senate," Biden said.

Political headwinds normally work against the party of incumbent presidents in their first midterm elections. According to an analysis by former George W. Bush administration official Bruce Mehlman, in the past 11 such midterm seasons, new presidents saw their party make net gains only twice in the House, four times in the Senate and zero times in state gubernatorial contests.

However, Fox News battleground polls released last week show a marked increase in Republican voter enthusiasm in the wake of the heated and bitterly partisan confirmation battle over Supreme Court Associate Justice Brett Kavanaugh.

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That enthusiasm has strengthened Republicans' already-strong odds of retaining control of the Senate, even as the House remains contentious.

"President Trump is the only president — and I've been there for nine now — who when things are going very well in terms of the economy, his numbers aren’t going up," Biden said Wednesday.

Still, poll numbers for Republican Senate candidates have become significantly more favorable. Compared with early September, the number of Republican voters feeling “extremely” interested in the upcoming election is up by 2 points in Arizona, up by 9 points in Indiana, up 8 points in both Missouri and North Dakota, and up 11 points in Tennessee. In each state, Republicans are now just as likely as Democrats to say they are extremely interested -- erasing an edge Democrats had in several states last month.

"The fight over Judge Kavanaugh is increasing base intensity for both parties, helping Democrats with white college-educated women in suburban House districts while bolstering Republicans among evangelical voters in the many rural red state Senate contests," Mehlman told Fox News.

Biden, who has repeatedly refused to rule out a 2020 presidential run in the past year, was briefly considered a possible challenger to Trump during the 2016 campaign. However, he ultimately decided to back eventual nominee Hillary Clinton, saying it would have been taxing to mount a campaign so soon after the 2015 death of his 46-year-old son Beau.