The impact of a constitutional issue depends on the issue. For example, a Fourth Amendment issue results in the suppression of the field sobriety test results. That can lead to the suppression of any breath test that was taken or administered. This suppression of evidence can bolster a Washington DC DUI defense.
Furthermore, when evidence is suppressed, the government may be unable to proceed with their case, resulting in a dismissal of the case. It can so severely hamper the government’s case, they are unable to proceed successfully.