American Bitcoin, the Trump-family-backed mining venture, swung to a roughly $126 million profit in the third quarter, a sharp reversal from the loss it posted three months earlier, as a jump in Bitcoin’s book value and disciplined accumulation powered its best showing yet. The Nasdaq-listed company, which trades under the ticker ABTC and is majority-owned by miner Hut 8, reported net income of about $126 million for the quarter ended Sept. 30, compared with a $57.2 million net loss in the second quarter.