U.S. stocks closed narrowly mixed near record levels Thursday as earnings season got underway, amid renewed uncertainty about the Trump administration's ability to implement its pro-growth proposals.

Bloomberg reported that special counsel Robert Mueller is looking into the business dealings of President Donald Trump, Jared Kushner and other associates. This comes a day after Trump warned Muller against it during an interview with the New York Times on Wednesday.

The three major indexes hit session lows on the report before bouncing back.

The Nasdaq composite closed up 0.08 percent at 6390, a record close and its first 10-day win streak since February 2015. The iShares Nasdaq Biotechnology ETF (IBB) closed up 1 percent, while Apple fell half a percent.

The Nasdaq also hit an all-time high of 6,398.26 earlier in the session.

"Every day it seems like one or two components that drag the Dow, and the S&P and Nasdaq hit record highs because on balance, earnings season's going well," said Art Hogan, chief market strategist at Wunderlich Securities. "It feels like you've got a real focused shift from the macro to the micro."

The hit an all-time high of 2,477.62 but came less than a point shy of closing at a record, falling 0.02 percent to 2,473.45. Telecommunications led four sectors higher, while materials was the greatest decliner.

The Dow Jones industrial average lagged the S&P and the Nasdaq, closing nearly 29 points lower, or 0.13 percent, at 21,611.78.

Home Depot fell 4 percent as the greatest contributor to losses on the index after Sears said it will sell Alexa-enabled appliances on Amazon. Sears shares closed up 10.6 percent on the news.

UnitedHealth was the greatest contributor to gains in the Dow. The index closed within a third of a percent of its all-time high.