Nike stock has tumbled below $40 (£29.55) for the first time in roughly 12 years, leaving Wall Street's mostly bullish analysts under pressure as the athletic giant's turnaround stalls. Shares slid 4.03% on Monday to close at $39.09 (£28.88), marking their lowest closing level since 2014 and extending a brutal slide that has erased roughly 78% of the stock's value since its record high of $177.51 (£131.17) in November 2021. Nike's fiscal fourth-…