(This is the Warren Buffett Watch newsletter, news and analysis on all things Warren Buffett and Berkshire Hathaway. You can sign up here to receive it every Friday evening in your inbox.) Berkshire trails red-hot S&P by biggest margin so far this year With  hot tech stocks  fueling its solid 5.1% gain in May, the  S&P 500  closed Friday at a  fresh record high . In a sharp contrast, shares of Berkshire Hathaway were close to unchanged for the month. As a result, Berkshire's widely held  B shares  are now running 16.3 percentage points behind the benchmark index year-to-date, the biggest gap so far in 2026. At the end of March, Berkshire had a small winning margin of 1.8 percentage points over the S&P. But then the S&P zoomed more than 35% higher in April and May while Berkshire fell almost 11%.…