Barack Obama has regained momentum in his campaign to become the Democratic candidate in the race for the White House. The state of Pennsylvania goes to the polls on Tuesday, in what is the biggest remaining primary. It may prove to be the deciding factor

Obama’s meeting with his supporters in Philadelphia attracted the largest crowd ever to attend an Obama event. Around 35,000 people jammed into a downtown park to hear his message of change.

“This year we can't afford the same old policies. This year we have to declare our independence from this kind of politics. That's the chance we have and the choice you face next Tuesday,” Obama said.

Next Tuesday, April 22, is when Pennsylvania voters head to the polls to pick a Democratic nominee. Victory in the crucial primary could mean winning the race for the White House. And Obama isn’t taking anything for granted.

The Philadelphia rally is part of a five-day tour to win more voters or simply to persuade more Hillary Clinton supporters to switch camps.

Obama used the meeting not only to attack his Democratic rival but also to hit out at the Republican nominee.

“I don't think we can afford four more years of George W. Bush and McCain ideas of progress. It's time to turn a new page in American history,” he said.

Obama had lost some of his lead earlier in the week, after a debate with Hillary Clinton.

But the latest polls suggest he is once again regaining ground, after turning some of the negative attacks to his favour.