Stocks defy tariffs, DeepSeek drama to post best presidential term start since 2013 - MarketWatch

1. Nvidia lost over $590 billion in market cap amid AI development concerns. 2. Trump announced tariffs, causing nervousness but no panic among investors. 3. S&P 500 had its best start since Obama's second term despite tariffs. 4. Investor psychology remains optimistic, viewing dips as buying opportunities. 5. Elevated interest rates may limit equity multiples; earnings growth is essential.