But deterrence has been spotty. In the Democratic National Committee case, two senior administration officials spoke on the condition of anonymity to discuss the options, ranging from countercyberattacks on the F.S.B. and the G.R.U., two competing Russian spy agencies at the center of the current hacking, to economic, travel and other sanctions aimed at suspected perpetrators.

At the event in Aspen on Saturday afternoon, Lisa O. Monaco, Mr. Obama’s homeland security adviser, sidestepped specific discussion of the D.N.C. hacking but acknowledged that the administration might soon have to consider whether the United States’ electoral system constitutes “critical infrastructure,” like the power grid or the cellphone network.

“I think it’s a serious question,” she said, especially if there is “coercion, destruction, manipulation of data.” Ms. Monaco noted that whenever the United States thinks about retaliation, “the danger of escalation and misinterpretation is such that we have to be responsible about it.” But she also said that if an event were serious enough, “we have to be very clear we will respond.”

The cost of doing nothing could be high. As the United States and other nations move to more electronic voting systems, the opportunities for mischief rise. Imagine, for example, a vote as close as the 2000 presidential election between George W. Bush and Al Gore, but with accusations about impossible-to-trace foreign manipulation of the ballots or the vote count, leaving Americans wondering about the validity of the outcome.