Sen. Elizabeth Warren, stepping up her crusade against the power of wealthy interests, accused a Brookings Institution scholar of writing a research paper to benefit his corporate patrons. Warren's charge prompted a swift response, with Brookings seeking and receiving the resignation of the economist, Robert Litan, whose report criticized a Warren-backed consumer-protection rule targeting the financial services industry. Warren leveled her criticisms in letters sent Tuesday to Brookings leaders and the Obama administration, citing the $85,000 combined fee that Litan and a co-author received from [Capital Group, a leading mutual fund manager]. Warren called the report highly compensated and editorially compromised work on behalf of an industry player seeking a specific conclusion." Her complaint pointed to a relatively new form of influence peddling in the nation's capital, with industry groups and even foreign governments paying think tanks and scholars for research papers that support lobbying goals. Brookings over the past decade has embarked on aggressive fundraising drives to pay for major expansions. Investigations last year by The Washington Post, the New York Times and others found that donors had gained the ability to influence Brookings's events and research agenda.