WASHINGTON » President Barack Obama said today he has seen no evidence that national security was threatened by the widening sex scandal that ensnared his former CIA director and top military commander in Afghanistan.

In his first postelection news conference, Obama also reaffirmed his belief that the U.S. can’t afford to continue tax cuts for the wealthiest Americans, a key sticking point in negotiations with Republicans over the impending "fiscal cliff."

The tangled email scandal that cost David Petraeus his CIA career and led to an investigation of Gen. John Allen has disrupted Obama’s plans to keep a narrow focus on the economy coming out of last week’s election. And it has overshadowed his efforts to build support behind his re-election pledge to make the wealthy pay more in taxes in order to reduce the federal deficit.

Obama said he hoped the scandal would be a "single side note" in Petraeus’ otherwise extraordinary career.

Petraeus resigned as head of the CIA last Friday because of an extramarital affair with his biographer, Paula Broadwell, who U.S. officials say sent harassing emails to a woman she viewed as a rival for the former general’s affection. The investigation revealed that that woman, Jill Kelley, also exchanged sometimes-flirtatious messages with Allen.

Obama brushed aside questions about whether he was informed about the FBI investigations that led to the disclosures quickly enough. White House officials first learned about the investigations last Wednesday, the day after the election, and Obama was alerted the following day.

"My expectation is that they follow the protocols that they’ve already established," Obama said. "One of the challenges here is that we’re not supposed to meddle in criminal investigations and that’s been our practice."

Turning back to the economy, the president vowed not to cave to Republicans who have pressed for tax cuts first passed by George W. Bush to be extended for all income earners. Obama has long opposed extending the cuts for families making more than $250,000 a year, but he gave into GOP demands in 2010 when the cuts were up for renewal.

That won’t happen this time around, he said today.

"Two years ago the economy was in a different situation," Obama said. "But what I said at the time was what I meant. Which was this is a one-time proposition."

The president and Congress are also seeking to avoid across-the-board spending cuts scheduled to take effect because lawmakers failed to reach a deal to reduce the federal deficit. Failure to act would lead to spending cuts and higher taxes on all Americans, with middle-income families paying an average of about $2,000 more next year, according to the nonpartisan Tax Policy Center.