In Mrs. Clinton's years away from politics, income inequality has become a defining political issue in the Democratic Party, elevating a new generation of stars like Senator Elizabeth Warren of Massachusetts, who has pushed for the breakup of large financial institutions.
Late last month, Ms. Warren campaigned in Kentucky for Alison Lundergan Grimes, the Democratic candidate for Senate, a sign that some in the party believe the Massachusetts senator's message resonates well beyond the left. (Mrs. Clinton has not yet campaigned on behalf of Ms. Grimes, though an adviser said she will likely do so this fall.)
"I think there's a potential window for Democrats to come back, but if it is one wing of the party pushing the populist line — anti-big banks, punishing people whether or not they had anything to do with the crisis — they'll lock this crowd into a Republican alternative," said Bill Daley, a former chief of staff to Mr. Obama and commerce secretary under President Bill Clinton who is now a hedge fund executive.
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During her 2008 primary campaign against Mr. Obama, Mrs. Clinton emphasized her husband's economic record. But running on the 1990s will not work in 2016, Mr. Daley suggested. "She has to figure out where she is going forward," Mr. Daley said.
At stake is not merely tens of millions of dollars in campaign money, but the shape of debates about social mobility, taxation and regulation. In the next few years, lawmakers may consider proposals to allow American corporations to "repatriate" overseas income at a reduced tax rate; change how the government backs home mortgages; eliminate the "carried interest" loophole that allows private equity managers to avoid paying higher tax rates; and more tightly regulate commodities trading.
"Secretary Clinton's time in the Senate was characterized by a willingness to work with all of the stakeholders, but she left the Senate just as the crisis was hitting its low point," said Francis Creighton, the top lobbyist for the Financial Services Roundtable, a trade association representing the largest banks and financial firms. "As an industry, we're not sure how her views have evolved over the last five years on what we do. The question is: Will her perspective have changed?"
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The last time Mrs. Clinton waded deeply into these issues, she was locked in a heated primary and the country was on the verge of the worst economic crisis since the Great Depression. She was early to call for tougher regulation of financial derivatives and private-equity markets, and in a 2007 speech called for major federal intervention in the market for subprime loans, arguing that "we need to acknowledge that Wall Street has played a significant role in our current problems, and in particular the housing crisis."
Several people who advised Mrs. Clinton on her 2008 presidential campaign said the speech angered some of her Wall Street donors, who complained about what they viewed as her increasing antagonism to the industry. Mrs. Clinton has also called for eliminating the carried interest tax loophole.
"If you look at her positions, in my view, she was very aggressive on ensuring that Wall Street was better regulated and her argument about all these proposals is that this is going to be better for all of us," said Neera Tanden, who was Mrs. Clinton's policy director during the 2008 campaign.
A spokesman for Mrs. Clinton, Nick Merrill, declined to describe her positions on a variety of current regulatory and Wall Street issues but said in an email: "Reducing inequality and increasing upward mobility has been an uninterrupted pursuit of hers through every job she's held, and it continues to this day in her work at the Clinton Foundation."
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If Mrs. Clinton runs for president, she will step into a heated debate about the interplay between financial regulation, growing inequality and the economic squeeze of the middle class.
The Third Way, a center-left think tank founded by two former Clinton administration aides, has assailed Ms. Warren, saying her economic populism would be "disastrous for Democrats."
As Democrats debate whether to get tougher on Wall Street, the industry appears to have taken notice. Securities and investment firm employees have given a smaller proportion of their political donations to Democrats over the last three years than any period for which data is available, according to the Center for Responsive Politics.