The S&P 500 was down 0.4% in midday trading to 2,028.55.
The Dow Jones Industrial Average was down 0.3% to 17,442.53.
The NASDAQ was down 0.3% to 4,755.57.
The yield on a 10-year Treasury bond was up 1.2% to 1.90%.
The price of gold was down 0.2% to $1,221.
Aliso Viejo-based Microsemi Corp. was up 3.5% to $38.35 and a $4.3 billion market cap. The semiconductor maker will sell defense electronics industry businesses to Chelmsford, Mass.-based Mercury Systems Inc. for $300 million. The deal is expected to close in the third quarter.
Irvine-based Lombard Medical Inc. was up 40% to $1.15 and a $23 million market cap. The maker of endovascular stent-grafts for aortic aneurysms had traded shares by midday at a rate eight times higher than its 90-day average.