Markets were mixed on Tuesday.
The S&P 500 fell 0.1 percent but the Dow Jones Industrial Average rose 0.1 percent, its eighth consecutive gain and its sixth consecutive record close.
Elsewhere, the STOXX Europe 600 fell 0.4 percent but the Nikkei 225 jumped 1.4 percent.
The WSJ's MoneyBeat blog pointed out that US stocks "are looking as stretched as they've been in more than five years", with the S&P 500 P/E ratio at 19.4, the highest since February 2010.
Nevertheless, some analysts think that stock valuations could remain elevated for a while yet. As Convergex noted, US stocks are "the only game in town".