President Barack Obama officially launched his campaign for re-election in November with a rally in Columbus, Ohio, on Saturday.
He told supporters the United States has been fighting its way back from economic recession under his leadership, and victory is crucial.
His re-election effort was formally launched last year, but official political events have been confined to fundraisers since then.
Mr Obama criticised Republican challenger Mitt Romney saying he would reverse the gains his administration has achieved.
"We were there, we remember, and we are not going back - we are moving this country forward," Obama said.
"Forward" is the campaign's latest slogan and people in the crowd held signs with that word above their heads.
Ohio has 18 votes in the electoral college. Unemployment there was 7.5% in March, below the national average, which was 8.2% in March and 8.1% in April.
The election is on 6 November.