News - Middle East: Incumbent Joe Biden and former presidents Barack Obama and Donald Trump have each sounded the alarm over threats to "democracy" in the US as the countdown starts to the congressional midterm elections on Tuesday.

Biden, Obama and Trump all converged on Saturday on Pennsylvania to push their parties to the finishing line in a race that the incumbent described as a "defining" moment.

Pennsylvania is one of a handful of swing states that will decide the overall balance of power when US voters determine who will control Congress during the last two years of Biden's first term.

Speaking to thousands in a Philadelphia arena, Biden said US voters face "a choice between two vastly different visions of America."

"Democracy is literally on the ballot. This is a defining moment for the nation and we all, we all must speak with one voice," he said.

Obama, who is seen as the Democratic superstar, warned that "fundamental rights..., reason and decency are on the ballot."

He attacked the Republicans for being increasingly averse to everything from science to respect for rules.

"Democracy itself is on the ballot. The stakes are high," Obama said in an echo of Biden's warning, his voice going hoarse.

Police state

Trump blamed Biden for turning the country into a police state.

The former president called for a Republican "giant red wave" to defeat Democrats in the midterm elections.

"If you want to stop the destruction of our country and save the 'American Dream,' then this Tuesday you must vote Republican in a giant red wave," he told a rally, referring to the party's traditional color.

As they spoke, a Washington Post-ABC News poll showed more and more Americans are afraid that violence will break out in the country.