By Lewis Krauskopf NEW YORK (Reuters) -U.S. stocks have hit a string of record highs with minimal turbulence over the past few months, but investors say the rally could be undermined by persistently high inflation, possible earnings disappointments and elevated valuations. The S&P 500 has posted 25 record closing highs over the past three months and the benchmark index is approaching a third anniversary of a bull market that began on October 12, 2022. Stocks shook off fears that President Donald Trump ...