Trump is killing one of the most crowded, popular stock market trades: Amazon

Big investors are taking a large hit from the share drops in technology leaders over the past week, partly driven by President Donald Trump's tweets.

Bank of America Merrill Lynch told its clients that funds had significantly larger stakes in Amazon and Netflix compared to benchmark market indexes at the end of last month.

Trump has tweeted about Amazon multiple times in recent days. The president criticized the e-commerce retailer over taxes and claimed it has not paid the post office adequately for its delivery services, spurring a plunge in its stock price.

Amazon and Netflix shares are down more than 11 percent over the past week through midday Monday. Both stocks fell more than 4 percent Monday.

"In this month's fund holdings update, Consumer Discretionary remained the most crowded sector, as large cap fund managers modestly raised their relative exposure to a five-month high," strategist Savita Subramanian wrote in a note to clients Thursday. "But the overweight is almost entirely driven by Amazon and Netflix, which together account for ~25% of the sector's market cap."

The strategist noted half the mutual funds it tracked owned Amazon, while 23 percent owned Netflix. The average relative position size in Amazon versus the index was 1.7 times, while Netflix's weighting was 2.0 times the benchmark.

Subramanian's team aggregated all the positions from U.S. large-cap equity mutual funds, using FactSet institutional ownership data. They then compared the weightings versus the relevant equity index benchmark to calculate its "crowded" stock analysis.

She has said it's more difficult for crowded stocks to move higher since everyone is already in the trade. Moreover, when sentiment shifts there may be more downside risk as investors flee for the exits at once, according to Subramanian.