"The Russians have to be celebrating the success of what they set out to do with rather minimal resources and expenditure," he said at the hearing on Russia's influence during the election. "They're going to continue to do it, and why not? It proved successful."
Watch this: Former US intel chief says Russia will hack more elections
Meanwhile, Russia has also successfully hacked campaigns in Eastern Europe, Clapper said, such as ones Ukraine and Bulgaria. And emboldened by its success with the US presidential election, Russia allegedly tried influencing elections in Germany and France as well, Clapper said.
"If they can drive wedges between the European nations, particularly by manipulating and influencing elections, they're going to do it," Clapper said. The Russian hacker's arsenal includes paid trolls, hacking and leaking secret emails, he added.
Clapper said Congress' IT systems have been targeted and could be hit for future elections. He recommends countering the Russians by "giving them some of their own medicine" to deter future attacks.
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