I have thought the same thing about Michael Obama however I have never felt like she is even slightly interested in running.
She didn't want her husband to run to begin with.
I don't know her though, maybe I'm wrong...
If I were a liberal and I wanted to defeat Donald Trump, I would almost beg her to run because, again, I don't see anyone within the current field that have much of a chance. Bernie probably has a better chance than most. but I don't see where he can actually win today, opposed to 2016. As much as I loathed Barack Obama's policies, I will admit that people liked him and they loved Michelle. They felt as if the Obamas listened to them, understood their hardships, and they thought that they were able to relate to them on a personal level. If I remember correctly, the leadership of the Democrat party and the DNC did not want him (to begin with). They wanted Hillary because, again, the message was "it's her turn", as if it was coronation and not a primary election. Just like 2016, though, she lost on that platform, while Obama set himself up as likable, relatable, and knowledgeable.
Bernie did something similar, but I think Obama did it better. With Michelle, she can use that same formula but have it modified however she sees fit. If she did it exactly the way her husband did it, to the letter, she wouldn't do well. Michelle would need her own identity, while maintaining she is the wife of a former president. To me, all this makes sense. My prediction stands about Trump being re-elected, but let me add something to it so there's a little context. He would win IF Michelle Obama doesn't enter. It would practically be a guarantee. Not that I haven't thought this before about them, but the other candidates feel a little too much like your run in the mill politicians out of Washington D.C. and don't appear genuine (with the exception of Bernie and MAYBE Biden). It's as if they're ONLY after your votes and don't want to actually work for you. In addition, a lot of their focus would probably be focused more on Trump than actual policy, which could go terribly wrong if they did that. Michelle Obama, I think, would be a different story. Now, I am a conservative and I'm not going to say that if she entered she would be the next president. I still think Trump would have the advantage, but she would definitely be the greatest threat in 2020 if she ran. That's just me, and if she did run, she could win everything. But again, we'll see what happens.