A 2015 Chinese-backed cyberattack on the Office of Personnel Management that exposed millions of personal records was "materially different" than the Russian-backed cyberattacks on Democrats during the election cycle, which is why the White House cracked down harder on the latter breach, press secretary Josh Earnest said Tuesday.

"What we've seen is that these are two cyber incidents that are malicious in nature but materially different," Earnest said, defending the administration's decision to issue sanctions in response to the Russian hack but not the Chinese hack.

The OPM hack was one of the largest data breaches in the history of the United States. More than 20 million people were affected, with the Chinese gaining possession of names, Social Security numbers, dates of birth, places of residence, and sensitive information from background investigations.

"I'm just saying that it's different than seeking to interfere in the conduct of a U.S. national election," Earnest said.

Last week, the White House unveiled a round of sanctions against actors accused of orchestrating cyberattacks on the Democratic National Committee, the Democratic Congressional Campaign Committee and several prominent Democratic operatives. The retaliatory measures included the immediate ejection of 35 Russian diplomats currently residing in the U.S.

"There's no denying that this is a significant action," Earnest said of the Russian sanctions, arguing the Kremlin had directed an effort "to try to influence our democracy."

Earnest rejected the suggestion that the U.S. had allowed the Chinese hacks to proceed unchecked.

"I can't speak to what response might have been initiated in private," he said. Earnest noted that Chinese leadership has since agreed to abide by "norms" in cyberspace.