CHICAGO — US President Joe Biden cemented the Democratic Party's elevation of Kamala Harris to lead the fight for the White House against Republican Donald Trump during a convention speech on Monday, as thousands of pro-Palestinian demonstrators marched near the venue to express their dissatisfaction with the Biden administration's handling of the Israeli-Palestinian conflict.

Biden took center stage on the opening night of the Democratic National Convention, delivering a farewell speech to the party he has served for half a century. He has five months left in office.

Taking multiple swipes at Trump, Biden promised to be the "best volunteer" Harris and Minnesota Governor Tim Walz, her vice-presidential running mate, had ever seen.

Biden's address in Chicago kicked off a four-day event fueled by enthusiasm for Harris and relief that Biden abandoned his own reelection bid and endorsed her to replace him.

Biden urged Democrats to unite behind a candidate who, if triumphant on Nov 5, would become the first woman, who is also black and South Asian, to be elected US president.

Harris is riding a historic whirlwind into the convention: her campaign has broken fundraising records, packed arenas with supporters, and turned opinion polls in some battleground states in Democrats' favor.

She joined Biden onstage for a hug after he finished his address on Monday.

Harris' campaign said on Monday that she is proposing to increase the corporate tax rate to 28 percent from 21 percent if she wins the election against Trump.

Harris campaign spokesman James Singer said the move would be part of "a fiscally responsible way to put money back in the pockets of working people and ensure billionaires and big corporations pay their fair share".

When Trump was president, he slashed the corporate tax rate to 21 percent from 35 percent and implemented other tax breaks that are set to expire next year. Trump has vowed to make the cuts permanent.

The Committee for a Responsible Federal Budget, a nonpartisan advocacy group, said on Monday that Harris' proposal to raise the corporate income tax rate to 28 percent would reduce the US deficit by $1 trillion over a decade.

As Democrats gathered for the convention, Trump took to social media to criticize his opponent.

"Kamala Harris can't answer how she'd pay for any of her new liberal spending schemes that will bankrupt our country!" Trump said in a post on Truth Social.

Tight race

In the key swing states that could decide the results of the election, the race between the two remains tight.

According to the latest poll data compiled by RealClearPolitics, Harris leads Trump by 1.0 percentage points in Wisconsin and by 2.0 percentage points in Michigan. In Pennsylvania, Harris trails by 0.2 percentage points.

While the Democrats were gathering for their convention, thousands of pro-Palestinian protesters marched in a neighborhood park to voice their discontent and anger toward the Biden administration's Israel policy, as the Palestinian death toll from Israeli attacks on the Gaza Strip has surpassed 40,000 since the outbreak of the current conflict on Oct 7.

After hours of peaceful demonstrations, dozens of protesters broke through part of the perimeter security fence, drawing riot police to the site, a Reuters witness said.

The convention's security team confirmed that protesters breached a portion of the fencing on the outer perimeter near the convention arena but said law enforcement personnel acted quickly and there was no threat to attendees.

Reuters witnesses saw four people detained and handcuffed. Chicago police confirmed at a news conference that arrests were made but did not say how many.

The chanting intensified ahead of the fence breach, as protesters reached a neighborhood park on Chicago's West Side and paused to amplify their calls for a cease-fire.