(These are the market notes on today's action by Mike Santoli, CNBC's Senior Markets Commentator. See today's video update from Mike above.) New month, familiar market action. Uneven performance across sectors with a couple of mega-cap AI proxies supporting the S & P 500 while overall breadth struggles and old-economy cyclicals struggle a bit. The character of Monday's session, and the past week, has done little to quiet the voices declaring that subpar market breadth, severe index concentration and myopic enthusiasm toward the AI infrastructure theme are making the market unbalanced and vulnerable. Yet the broad uptrend has held, year-end tendencies favor a further advance and earnings in aggregate are coming through just fine. The generic setup is well understood: Good years tend to fini

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