Trevor Williams | DigitalVision | Getty ImagesThe S&P 500 index closed at a new all-time high on Wednesday amid a federal government shutdown. It rose to a new intraday high early Thursday.Prior to that, the index — which is focused on large-cap U.S. equities — had risen almost 90% since the equity bull market began three years ago, thanks in large part to new AI developments, Morgan Stanley Wealth Management noted in Sept. 29 research.Nevertheless, experts say it may be time to reconsider the set-it-and-fo ...