Roll Call explains:

Sen. John McCain’s victory in the Aug. 24 Arizona Republican primary was fueled partly by transfers of $7.5 million from his 2008 presidential campaign compliance fund — an account GOP Congressional strategists are now eyeing as they look to finance a growing list of competitive midterm races.

McCain’s compliance fund reported $17.1 million in cash on hand as of June 30, with $4.65 million in transfers to the Senator’s re-election committee having been made during the second quarter of this year. Additional transfers were made before the August pre-primary fundraising reporting deadline. McCain also used the compliance account to make $63,900 in charitable donations to the Boys & Girls Clubs of Phoenix and about a dozen Phoenix-area churches.

Any presidential candidate who participates in the public financing program must submit to a post-election audit of his campaign operation by the Federal Election Commission. McCain’s compliance fund, officially known as the McCain-Palin Compliance Fund Inc., was assembled to cover the accounting and legal fees generated by that audit.

However, excess funds from compliance accounts are available to be transferred to other campaign committees or for charitable donations.