Warren Buffett's Berkshire Hathaway remains undeterred by the recent US downgrade by Fitch Ratings. Buffett invested $10 billion in US Treasuries and plans to invest another $10 billion, unfazed by concerns. Fitch downgraded due to deficit worries and political tensions. Contrasting Buffett's approach, Bill Ackman of Pershing Square Capital Management took a significant short position on 30-year Treasuries as a hedge against potential stock market impact from higher long-term rates.