Boeing Co.'s stock BA, -3.81% slid 1.7% in morning trade, and was the biggest reason for the Dow Jones Industrial Average's DJIA, -0.87% decline early Thursday, as it took a breather following its recent stellar run to record highs. Boeing's price decline of $5.86 was shaving about 40 points off the Dow's price, which was down about 4 points. Despite the pullback, the aerospace and defense contractor's stock was still the best performer in 2018, with a 16.6% gain. The stock's $50.24 price gain year to date has added about 346 points to the Dow, which is up about 1,393 points so far this year. The next-best year-to-date performer was International Business Machines Corp. shares IBM, -1.72% , which had climbed 11% so far this year.