Investing the US has rarely been this popular, and exchange-traded funds have been the investment vehicle of choice. Traders poured $23.56 billion into US funds and ETFs during the week ended Wednesday, less than $1.5 billion shy of the all-time record seen in March 2015, according to data compiled by a group of Bank of America Merrill Lynch analysts led by Yunyi Zhang. That marked a large step up from the prior week, which saw inflows of $1.13 billion, the data show. Much of the weekly surge came in the form of stock investments as $17.6 billion flowed into equity funds, the most this year.