(Bloomberg) — US stocks are heading into 2026 with positive momentum and a host of bullish forecasts at their backs. For the fourth year of strong gains that many predict to play out, they must still overcome plenty of potential threats. For a start, valuations are already rich and the group of stocks leading the gains is relatively narrow, a risky setup in itself. A lot is riding on artificial intelligence winners proving that, rather than forming a bubble, they have further to climb. Most Read from Bl ...