A new bipartisan poll in Wisconsin taken after the presidential debate on June 27 has former President Donald J. Trump up five percentage points against President Biden in the swing state, 50 percent to 45 percent. Mr. Biden was trailing by a similar margin — six percentage points — in a ballot that included third-party candidates, which had the independent candidate Robert F. Kennedy Jr. at 9 percent in the state.

Mr. Biden is running far behind Senator Tammy Baldwin, the Democratic incumbent, who has the support of 50 percent of likely voters in her race against her Republican challenger, Eric Hovde.

The poll, conducted by Fabrizio Ward and Impact Research on behalf of AARP, had Mr. Biden trailing Mr. Trump by an even wider margin — seven percentage points — among voters in the state who are 50 and older.

Mr. Biden’s weakness with younger voters was apparent in the poll. He is neck and neck with Mr. Trump among voters under 50, losing by just one percentage point, while Ms. Baldwin is winning the group by 14 percentage points.

Much of Mr. Trump’s strength in the state, according to the new poll, comes from consolidating Republican support: Mr. Trump is winning 93 percent of Republicans in a multicandidate field, while Mr. Biden is winning 86 percent of Democrats in such a field. Ten percent of Wisconsin Democrats say they plan to support a third-party candidate.

Views of Mr. Trump’s time in office are also helping to lift the former president’s candidacy. Just over half of Wisconsin voters strongly approve of Mr. Trump’s time in office, compared with 39 percent who strongly approve of Mr. Biden’s job performance.

The poll shows that nearly every demographic group feels that Mr. Trump won the debate last month. Swing voters over 50, a key focus of the poll, thought Mr. Trump won the debate by a wide margin.