The former President on Wednesday released four years of pent-up frustration in a scathing Philadelphia appearance that is likely to further irk an already irritable commander-in-chief ahead of his showdown with Democratic nominee Joe Biden. The debate in Nashville, Tennessee, comes at a fateful moment in the White House race as fresh polls emphasize the task Trump faces in pulling off another shock election triumph in 12 days.

In a new CNN/SSRS survey, Biden leads comfortably in Pennsylvania, potentially the decisive swing state, with a clear path to 270 electoral votes if he converts leads in Wisconsin and Michigan into wins. That leaves Trump needing the kind of late surge that took him to a stunning 2016 victory over Democrat Hillary Clinton. It also means his clash with Biden, already crucial given that their second debate was canceled after his Covid-19 diagnosis, could be a final opportunity to shake up the race.

But with a staggering 40 million early votes cast, the capacity of either candidate to change the dynamics of the election is becoming increasingly limited. As he geared up for the debate, Trump slammed the whole exercise as unfair, resentful about at a plan to periodically mute the candidates' mics designed to limit his belligerent interruptions and baselessly accusing moderator Kristen Welker of NBC of bias.

He is likely to have been especially infuriated by Obama's mockery and forensic dismissal of his record given his contempt for, and obsession with, the former President. Obama's appearance on the eve of a debate in which Trump's hair-trigger temper will be sorely tested was probably not a coincidence.

In another development on Wednesday, federal officials said that both Iran and Russia have obtained US voter registration information in an effort to interfere in the election. They said Islamic Republic operatives posed as the far-right Proud Boys -- a group which Trump refused to fully repudiate during the last debate -- to send intimidating emails to voters.

Director of National Intelligence John Ratcliffe said Iran's intent was to damage the President. Democrats and former officials in the covert officials will view his statement through a political lens, given his failure to immediately provide evidence and his past efforts to politicize intelligence to help Trump.

'They would have called me Beijing Barry'

The 44th President pounced on Trump's admission that there is "not much" he would change in one of the world's least successful attempts to quell a virus that has killed more than 221,000 Americans and devastated the economy.

"Really? Not much? Nothing you can think of that could have helped some people keep their loved ones alive?" Obama, who came on stage wearing a face mask bearing the world "Vote."

"Joe's not going to screw up testing. He's not going to call scientists idiots. He's not going to host a super spreader event at the White House. Joe will get this pandemic under control," Obama said of the man he chose to be his vice president 12 years ago.

His intervention, an extrao

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Barack Obama: 'A More Perfect Union' (Full Speech)