Charles Gabriel, head of Washington research for the Wall Street firm Prudential, wrote this yesterday:

In the wake of the House page scandal, we are raising our odds of a Democratic House takeover to two in three (from 55 percent), while also predicting near-even (45 percent) chances for the Dems to retake the Senate. We also see the correspondingly higher odds of a control shift in BOTH chambers -- now 40 percent (from 30 percent).
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After a pretty good month of September for the GOP, the scandal has visibly thrown the party off message, and threatens to: 1) dominate precious remaining daily news cycles leading up to Election Day; 2) further demoralize the Republicans' religious/conservative base; 3) essentially cede to the Democrats Foley's previously invulnerable seat, if not others; and 4) finally put an edge on Dems' "culture of corruption" campaign themes that the alleged transgressions of Abramoff, DeLay, Ney, Cunningham, and others had failed to do.

And mind you, Wall Street strategists typically err or lean to the side of the Republicans, i.e. they're usually understating any negative GOP news or odds....