US stocks at risk of bear market and "lower returns in the next several years"

Markets were mixed on Tuesday.

The S&P 500 rose 0.3 percent and the Nikkei 225 rose 0.6 percent but the STOXX Europe 600 fell 0.3 percent.

BTIG chief equity and derivatives strategist Julisan Emanuel told CNBC on Tuesday that a full-blown economic cold war between the US and China could send stocks into a bear market.

Also on Tuesday, Vanguard Group CEO Tim Buckley told CNBC that the return of volatility is normal while Vanguard portfolio manager Gerry O'Reilly said to expect more of it.

Over the longer term, Vanguard chief investment officer Greg Davis said to "expect lower returns in the next several years" for the US stock market and expects international stocks to outperform.