The loan Hillary Clinton made to her campaign has given Barack Obama's campaign an opportunity to make the finances of the two Clintons a campaign issue, and it's clearly an opportunity the Obama camp plans to take advantage of.

On Thursday, Obama himself raised the issue. Without directly suggesting that Clinton should release her tax returns, he drew a contrast between himself and Clinton on the issue, saying to reporters, "I'll just say that I've released my tax returns. That's been a policy I've maintained consistently. I think the American people deserve to know where you get your income from. But I'll leave it up to you guys to chase it down."

But what a candidate cannot say, his or her surrogates can. The Trail, a Washington Post blog, has more direct comments that Bill Burton, Obama's press secretary, made Friday. "Why should Democratic voters have to wait until after the primary campaign is over to find out important information about Senator Clinton's finances that Senator Obama has already disclosed?" Burton asked. "For someone who claims to be fully vetted, hiding a campaign loan from voters until after Super Tuesday and refusing to release your tax returns until after the primary doesn't seem like the best way to prove that there are no surprises for the Republicans to find once they start digging."

Clinton staffers have said she will release the returns she filed jointly with her husband if she wins the Democratic nomination.