At Sabato’s Crystal Ball, Brendan Nyhan has a fascinating analysis of the absence of major scandals in the Obama administration, and of the likelihood that the political environment will soon produce one.
Nyhan defines “major scandal” as “a widespread elite perception of wrongdoing.” By that standard, Obama has done very well:

In the 1977-2008 period, the longest that a president has gone without having a scandal featured in a front-page Washington Post article is 34 months – the period between when President Bush took office in January 2001 and the Valerie Plame scandal in October 2003. Obama has already made it almost as long despite the lack of a comparable event to the September 11 terrorist attacks.

Nyan believes the availability of competing news has a big impact on the emergence of scandals, and that Obama (like Bush) has benefitted from big, dominant developments that inhibited the growth of reports, rumors or smears into scandals. But totally aside from any assessments of its integrity, the Obama administration is overdue in the scandal department, particularly since opposition hostility is a big factor in increasing the likelihood of scandals:

Obama already faces low approval among GOP identifiers and a similarly hostile climate in Congress. Back in March, New York Times columnist Paul Krugman noted that Republicans hadn’t yet made a serious effort to back up claims that the Obama White House is “one of the most corrupt administrations.” As more time passes, pressure to find evidence of misconduct is likely to build — my data suggest that the risk of scandal increases dramatically as the period without a scandal stretches beyond two years.

Indeed, notes Nyhan, Republicans are already busily trying to fan the flames beneath a number of “stories” that could theoretically become “scandals:”

Recent examples include allegations of an administration “enemies list” as a result of a National Labor Relations Board complaint against Boeing; claims of favoritism in decisions to grant waivers from regulations imposed under health care reform; and allegations that Department of Justice officials allowed straw purchases of guns that were smuggled to Mexico, prompting a standoff with Congress that House Committee on Oversight and Government Reform Chairman Rep. Darrell Issa (R-CA) recently compared to Iran-Contra.

Since a couple of weeks of concentrated conservative media hyperventilation coordinated with, say, a congressional hearing, are entirely capable of moving just about any negative “story” to the threshold of a scandal, the key variable could actually be which mini-scandal the Right decides to make an obsession. If Nyhan is correct, that should happen pretty soon, absent another competing mega-story.