Public money supplied to campaign funds that match donations made by individual contributors up to a maximum of $250 per donation.

Candidates are not obliged to take matching funds, but if they do, they must restrict their spending to a maximum of approximately $40m during the presidential primary period.

Democrats and Republicans are automatically entitled to a public grant to pay for the cost of conventions. Minor parties are also entitled to a smaller subsidy in proportion to the vote they received. New parties are not eligible.