Mr McCain announces the temporary suspension of his campaign
The two US presidential candidates are in sharp disagreement over whether to postpone a TV debate in light of the country's economic crisis.
Republican John McCain said he was suspending his campaign to return to Washington to deal with the crisis.
But Democratic rival Barack Obama said it was "more important than ever" for US citizens to hear from the person who would soon be "dealing with this mess".
The two men are due to go head-to-head in their first debate on Friday.
On Thursday, they will meet US President George W Bush to discuss the proposed $700bn (£378bn) bail-out of the financial markets, which is set to go before Congress.
Mr Bush said in a televised debate on Wednesday that the entire economy was in danger and failure to act now would cost more later.
Shortly before his address, the two presidential hopefuls issued a joint statement, saying: "Now is time to come together - Democrats and Republicans - in a spirit of co-operation for the sake of the American people."
Mr McCain, on Wednesday, said he was suspending his campaign and called for the candidates' first debate - due to be held in Mississippi - to be delayed so they could focus on the financial crisis.
Barack Obama says he is still planning to attend Friday's debate
He said the $700bn bail-out plan was in danger of being defeated in Congress.
The BBC's Kevin Connolly in Washington says Mr McCain billed his dramatic move as a gesture above party politics at a moment of national crisis.
But, our correspondent says, it was smart tactics too because it conveyed a sense that Mr McCain was taking the lead on an issue where so far voters appear to have been finding Barack Obama more convincing.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.