It's national tax day, and in honor of this event Hillary Clinton's campaign began its conference call with reporters by calling on Barack Obama to release his tax returns from the late 1990s.

"Senator Obama, despite his rhetoric, does not appear to be abiding by the same standards that he has set for our campaign," said Phil Singer, Clinton's deputy communications director, regarding Obama's call on Clinton to release her tax returns. "He has refused to release his tax returns for 1997, 1998 and 1999, even though he was in public life during those years. And during that period of time he was accepting campaign contributions from lobbyists representing special interests, PACs, and even directly from corporations. We think that if Senator Obama is going to set a standard for our campaign certainly he should be following that same standard."

Arguing against the Obama campaign's claim of being transparent, Singer said, "When it comes to transparency, the only thing transparent about Senator Obama is the claim that he is transparent."

Clinton communications director Howard Wolfson played up the angle that because Obama is outspending Clinton in Pennsylvania by large sums, he is attempting to win the state and therefore cannot claim some moral victory if he loses on April 22. Wolfson said that if Obama "fails to win in Pennsylvania, it will be a significant defeat for him."

Wolfson even gave exact numbers for how much Obama was spending on TV ads, and compared it to Clinton's TV ad buys. Wolfson said Obama spent $3.3 million worth of TV ads in the state this week, outspending Clinton by two-to-one.

"Make no mistake, Senator Obama is competing full-bore in Pennsylvania," Wolfson said. "He's doing everything he can to win Pennsylvania."

Singer and Wolfson, after being questioned, also said that Obama's "bitter" and "cling" comments were an important issue that the campaign would continue to discuss. They also accused Obama's campaign of focusing on other elements of the controversial statement in a recent fundraising letter to supporters, rather than the words that have caused the controversy.

After calling Obama "detached," the two spokesmen were later asked if it was dangerous for Clinton -- who along with her husband has made more than $100 million since leaving the White House -- to say that any of her opponents are disconnected from working Americans.

Wolfson answered by comparing the Clinton's financial situation with previous presidents. "There is a long tradition of presidents in this country -- Franklin Roosevelt would be one, John Kennedy another --who have had personal wealth, being strong champions of working people, and being great presidents for working people."

On running a TV ad using "man on street" interviews with Pennsylvania residents regarding Obama's comments, Wolfson said, "We think that this is an important issue in the context of the race, and we're in the business of advertising issues that we think are important in the context of this race. And Senator Obama's comments…struck a nerve with many people in Pennsylvania. They found them condescending."