Bitcoin is back — and even bulls are befuddled.The controversial cryptocurrency surged more than 20 percent on Wednesday — briefly climbing as high as $13,879.24 in the afternoon — as investors scratched their heads over what might be driving the eye-popping rally.

Bitcoin had dropped nearly $2,000 by late afternoon to briefly trade below $12,000, but it was still changing hands at levels not seen since January 2018, when the digital currency was in the middle of a fast retreat from the all-time highs near $20,000 it notched in December 2017.

Bitcoin’s recent rally began to accelerate on June 18, when Facebook disclosed plans to launch its own cryptocurrency called Libra early next year. The announcement sparked hopes that the social-media platform with 2.4 billion active users could help bitcoin in its struggle to appeal to the mainstream.

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