Obama has raised more than $10 million, gave the keynote speech last month at the Democratic National Convention and is running in a Democratic-leaning state.
Keyes, a conservative Maryland political commentator, formally accepted the state's GOP nomination Sunday afternoon during a rally in Arlington Heights.
Keyes told Republican leaders he would turn to his national base of supporters, as well as to national party leaders, for financial help in the race.
On Friday, Keyes paid off the rest of his tax liabilities in Maryland, where he at one point owed more than $7,000, according to the state comptroller's office.
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