Dow Futures Plunge 300 Points Amidst Trump Tariff Uncertainty, Nvidia & Salesforce Results

• US stock futures fall, with Dow futures down 300 points, S&P 500 down 52, and Nasdaq down 250.
• Supreme Court ruled Trump administration's reciprocal tariffs illegal; Trump announced new 15% universal tariff.
• Uncertainty over potential tariff refunds, estimated between $85 billion to $175 billion, left to lower courts.
• Iran talks in Geneva on Thursday, Trump to decide on attack in 10-15 days; oil prices cool slightly.
• Key week for US markets: State of the Union address, Nvidia and Salesforce earnings, Fed official speeches, and PPI data.