Enduring Mind

You may concentrate on two spells at the same time. The combined level of these spells may be no more than half your level (rounded down) plus 1. 

For example, a level 11 wizard could concentrate on 2 spells with a combined level of not more than 6. This could be Blur, and Evard's Black Tentacles. An equivalent level ranger may choose to concentrate on both Hunter's Mark and Longstrider. 

If you are forced to make a concentration save you do so for all spells you are concentrating on simultaneously. 

You may not take both this feat and War Caster.