(Bloomberg) -- The S&P 500’s 9.6% rally in three weeks is looking increasingly unsustainable to some market watchers.Most Read from BloombergOpenAI Leaders' Efforts to Bring Back Altman Reach Impasse Over Board RoleOpenAI Board Urged by Microsoft, Investors to Restore AltmanThe Doomed Mission Behind Sam Altman's Shock Ouster From OpenAIAltman Sought Billions For Chip Venture Before OpenAI OusterArgentina Takes Leap Into Unknown With Javier Milei as PresidentConcerns about the gauge include the f