The first lady and her daughters plan to do some sightseeing during a weeklong visit.
Nearly 97 percent of Crimeans voted to secede from Ukraine, reports said.
“I’m not going to get into a game of hinting or indicating who might be next,” an aide said.
A meeting comes just before a deadline to complete talks on a framework for peace.
The senator said he didn't know how Obama's response "could have been any weaker."
He said the United States stands ready to impose further punishment in the days ahead.
The GOP senator said Russian President Vladimir Putin only understands "strength and power."
Daniel Rubinstein succeeds Robert Ford, who retired late last month.
The Republican said the missing plane could have landed somewhere as part of terror scheme.