I am looking for a phrase that is in the same spirit such as "single point of failure", or "bottleneck". Example:
Being two engineers short is <-term goes here-> in this situation. If we find two engineers, the project will meet the deadline.
Electric cars are improved enough to be on par with internal combustion engine cars. However, the long charging time is <-term goes here-> behind the problem that electric cars are not as widespread as internal combustion engine cars.