Hi Sandi,

It looks like your tomatoes may be infected with white rot (sclerotina sclerotiorum). It's a disease that can occur if you plant too early, when soil is very wet, or in soil where tomatoes have been grown before.

The tomato stems dry up and you may see white fuzz develop, as your second photo shows. 

The links below are a bit technical but you can see photos that look like your plants. Ignore the chemical recommendations; they're aimed more at commercial growers. It would be easiest for  you to pull these plants, discard them and replant in a different location where tomatoes haven't been grown for awhile. Clean up your vegetable gardens every fall, removing all shriveled leaves and stems. 

https://blogs.cornell.edu/livegpath/gallery/tomato/white-mold-on-tomatoes/

https://gardenerspath.com/how-to/disease-and-pests/sclerotinia-tomato/

I hope this helps. Good luck.