Armed with new-found proceeds from the tax bill, American consumers went shopping in May, driving retail sales — and economic growth — sharply higher. The economy in the second quarter is tracking close to 4 percent growth — a level President Donald Trump raved about last December, just before the tax bill was approved. At the same time, he had also told reporters he was holding out for a doubling of growth to 6 percent. For now, his 4 percent forecast is close to coming true on a quarterly basis, after strong retail sales data pushed up tracking GDP growth for the second quarter to about double the first quarter's level. The economy grew by 2.2 percent in the first quarter. CNBC/Moody's Analytics Rapid GDP Update reported economists' estimates of tracking GDP show average growth at 3.8 percent, following Thursday's retail sales report. Their actual forecasts, which take into account economic reports yet to be released, is running at an average 3.6 percent.

Shoppers leave Best Buy after purchasing merchandise in Los Angeles. Ronen Tivony | NurPhoto | Getty Images

Retail sales in May were up 0.8 percent, double what some economists expected. Without autos, sales were up 0.9 percent. "On the heels of this data we now estimate real GDP is expanding at a 4.0% annual rate in Q2, up from our prior estimate of 2.75% and almost twice the 2.2% growth rate experienced in Q1," wrote JP Morgan chief U.S. economist Michael Feroli. If the economy hits that growth rate, it would be the best since the third quarter of 2014. "The primary source of the acceleration in growth this quarter is the consumer, which looks to be expanding real outlays at a 3.7% rate in Q2 following an anemic 1.0% pace last quarter," Feroli added. "We had looked for a rebound in Q2, as some temporary drags waned and the tax cut boosted disposable incomes. In any event, consumers wasted no time enjoying their tax windfall, as the Q2 saving rate looks like it will revisit the lows for the cycle."

U.S. Quarterly GDP Growth