Since bridges are generally over-engineered, small cracks usually don’t add enough stress on their own to cause further cracking. But combined with the external forces that created the crack in the first place at some point they lead to progressively larger cracks. Then the stresses start accumulating on the part of the concrete that is still intact as the load shifts, and the process accelerates.
The Republicans and the Democrats are not the same. Underlying too much of contemporary reporting is a “false equivalency,” which posits that by representing “both sides” balance and objectivity are attained.