All three major US stock indexes were down in late-morning trading Monday after Moody's said late Friday it has downgraded the United States' credit rating.

Moody's on Friday lowered the long-term issuer and senior unsecured ratings of the US to Aa1 from Aaa, reflecting the increase in government debt and interest payment ratios over more than a decade "to levels that are significantly higher than similarly rated sovereigns."

In company news, Nippon Steel intends to invest $14 billion in US Steel's (X) operations, including up to $4 billion in a new steel mill, if President Donald Trump approves Nippon's bid for the company, Reuters reported Monday, citing a document and two people familiar with the matter. Shares of US Steel were up 1.7% around midday.

TXNM Energy (TXNM) said Monday it has agreed to be acquired by Blackstone (BX) Infrastructure for $61.25 per share in cash, reflecting a total enterprise value of $11.5 billion, including net debt and preferred stock. Blackstone is also investing $400 million through the purchase of 8 million newly issued TXNM common shares at $50 each in a private placement, with completion expected in June. TXNM shares were up 7.2%, while those of Blackstone were down 1.3%.

President Trump criticized Walmart (WMT) Saturday, accusing the retailer of using tariffs as an excuse to increase prices despite strong profits. Trump said in a post on Truth Social that Walmart shouldn't pass tariff-related costs onto consumers and instead should "eat the tariffs." Walmart shares were down 0.6%.

Qualcomm (QCOM) plans to launch a new central processing unit designed for data centers to power artificial intelligence that will connect to Nvidia's (NVDA) graphics processing units and software, Chief Executive Cristiano Amon said Monday in an interview on CNBC. Separately, Nvidia said Sunday it launched NVLink Fusion, a new silicon that helps build semicustom AI infrastructure. Qualcomm shares were down marginally, while those of Nvidia were up 0.1%.

Advanced Micro Devices (AMD) said Monday it has signed a definitive agreement to sell ZT Systems' data center infrastructure manufacturing business to Sanmina (SANM) in a cash-and-stock deal valued at $3 billion. AMD said it expects the transaction to be completed near the end of 2025. AMD shares were down 2.4%, while those of Sanmina were down 5.8%.

Novavax (NVAX) on Monday said it received approval from the US Food and Drug Administration for its biologics license application to use its Nuvaxovid COVID-19 vaccine in adults 65 years and older, as well as in individuals 12 through 64 with at least one underlying condition that puts them at high risk of severe illnesses from COVID. Novavax shares were up 16.6%.

Regeneron Pharmaceuticals (REGN) said Monday it has won the bankruptcy auction to acquire substantially all of the assets of 23andMe for $256 million. The acquisition includes 23andMe's Personal Genome Service, Total Health and Research Services units, its Biobank and related assets. The deal is expected to close in Q3, pending regulatory approvals and closing conditions. Regeneron shares were down 0.7%.

Price: 144.86, Change: -1.85, Percent Change: -1.26