Although late in terms of its potential impact on the Democratic presidential campaign, Sen. Hillary Rodham Clinton's release of her and her husband's federal income tax returns for the last eight years add a useful element to the picture that voters still face in the struggle for the nomination.

It is commendable that Mrs. Clinton released the returns, particularly since they revealed that the Clintons earned a level of income over the period, $109 million, that most Americans find too high to comprehend. In fairness, it is not extraordinary for former presidents to cash in on their periods in office through speeches, books, business ventures and other activities.

The prompt resignation over the weekend of Mrs. Clinton's chief campaign strategist, Mark Penn, because of his dual representation of her and Burson-Marsteller, a lobbyist for the Colombia free-trade bill, which she opposes, was also appropriate. The Colombian government had a $300,000-a-year contract with the New York-based public relations firm, of which Mr. Penn is chief executive. Mrs. Clinton could not have continued to court union members, a key group of supporters, while having as her chief adviser a lobbyist for the free-trade bill.

One important piece is still missing, however, in the picture that Mrs. Clinton presents to the electorate who are assessing her lines of influence, and, through them, her integrity. That is the list of donors and the amount of their donations to the foundation that built Mr. Clinton's presidential library in Little Rock, Ark., and funds his philanthropy. Absent that list, there will be the usual speculation that it includes names linked to those whom Mr. Clinton pardoned for crimes during his presidency and others to which the American electorate would not like to see their former or possibly future president indebted.

The only way Mrs. Clinton can clear the record on that is to release the list. She should do so as soon as possible, particularly since some Pennsylvania voters in the April 22 primary and politically professional superdelegates are still in the "undecided" column between her and Sen. Barack Obama.

Now that Mrs. Clinton has opened her tax returns, as did Mr. Obama previously, it's time for Sen. John McCain, the presumptive Republican nominee, to follow suit.