First Lady to give headline speech; will there be an empty chair at the DNC?

Here are some things to watch for at the Democratic National Convention on Tuesday:

1. THE DISAPPOINTMENT CHARGE: How will the first day's speakers address the Republican assertion that President Barack Obama's first term has been a "disappointment"? Will they tackle the notion head on?

2. THE FIRST LADY: Michelle Obama's main goal is to differentiate her husband from his Republican opponent, but she rarely mentions Mitt Romney by name. She'll wrap things up Tuesday night.

3. LONE STAR: The convention's keynote speaker, San Antonio Mayor Julian Castro, is a rising Democratic star, and some speculate he could become the next governor of Texas -- or even the first Hispanic president. 

4. ROMNEY, REMOTELY: What will we hear from the newly minted GOP nominee as his rival has a moment in the spotlight? What will the Republicans' "counter-programming" be during the Democratic convention?

5. THE EMPTY CHAIR: Can Democrats capitalize on Clint Eastwood's unusual pop-culture moment last week, or even make political hay out of it? Or would it be smarter to stay away?