Hi David. This looks like a fungal disease like Early Blight which is very common in tomatoes in Maryland when we have periods of cool, wet weather. You want to remove the affected branches as you see them and put them in the trash.  The plant should do fine if the disease doesn't progress too quickly.  Take a look at this information from the Cornell Cooperative Extension Service which gives advice on preventing the disease to see if there is something more you can do.
 
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PREVENTING DISEASE: Leaf Spot & Early Blight are two fungal diseases common to tomatoes. Leaf Spot spores live on infected plant debris in the nightshade family – potatoes, tomatoes, eggplants, and weeds like Datura, horsenettle, and black nightshade. They also survive on equipment like pruners, plant cages, and stakes. The fungus appears as numerous brown spots on the leaves. The leaves eventually turn yellow, then brown, and then die.

Early Blight spores live on infected plant debris and in the soil. They appear as irregular dark spots that continue to grow and are surrounded by a yellow ring. Eventually, the entire leaf blackens and dies. The fungus attacks all parts of the plant including the stems and fruit. The fruit eventually rots.

Both appear during warm humid weather and are exacerbated by long periods of rain or poor watering practices. Both begin on lower leaves & stems and spread upward. Both are spread by gardeners, tools, water, wind, and insects. Prevention is key because once your plants have fungus they cannot be cured. Once it takes hold, extra measures are consistently required to prevent the diseases from spreading. All of the garden practices mentioned below help reduce the spread of disease:

• Keep foliage dry. Water the soil and not the plants to keep water and splashing soil off the leaves.

• Improve air circulation by staking/caging and pruning out excessive leaf growth. You want the sun and wind to dry the foliage quickly after rain.

• Follow proper spacing guidelines to increase airflow between plants. Avoid putting plants too close together.

• Use mulch at the base of tomato plants. It limits soil and fungal spores from splashing up onto the plants and helps maintain soil temperature and moisture.

• Rotate your crops each year as the fungal spores overwinter in the soil.

• After use, wipe down your hands and pruners with alcohol-soaked wipes to limit the spread of the disease from one tomato plant to another.
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As for the mites, it would be better to spray your plants with a stream of water to knock them off, instead of using oils or soaps in the hot weather we are having now. 
Take a look at the MD HGIC website link below which has general instructions on growing tomatoes and see if there might be something you could add to your gardening practices that would help prevent problems. Remember to think about what types and specific species of tomatoes you are selecting to grow...maybe you could find ones that are more resistant to these diseases. 

https://extension.umd.edu/resource/growing-tomatoes-home-garden/

I hope this helps and that you end up with lots of tomatoes this year! Robin