First decide if you want to change state or federal law. Currently there is no Federal statute against drunk driving (unless the offense occurs on federal law).
Then you want to figure out how strict you want the law to be. Minimum jail time/fines, loss of driving priveledges, ect.
Once you've done that you can certainly try and gather like minded individuals and start lobbying either your local representatives if you want to change local/state law, or Congressperson if you want to change Federal law. The more people you have with you and the more awareness you can raise through the aforementioned petitions or protests, the easier it will be to grab a lawmaker's attention.
Alternatively you can find a lucrative career, make a truckload of money, and throw tons of cash into a Drunk Driving SuperPac.
Defamation suits are next to impossible to win....mostly because people don't understand what has to be proven, and don't understand why they actually don't have a case.
You need to prove the following to win the suit:
1. That the statement made was factual in nature, and not opinion or based on an observation (i.e. "Pete was convicted of a crime" is a factual statement; "Pete is a scumbag" is an opinion statement and not subject to any sort of lawsuit.)
2. That the statement was untrue.
3. That the speaker knew at the time it was said that the statement was untrue.
4. That you incurred actual financial losses because of what was said.
A rumor is not defamation, opinion statements are not defamation, true statements are not defamation. Also, proving actual financial losses is very difficult unless you lost a job or clients because of the statements. Hurt feelings and being upset are not financial damages. Even if the statement was factual and untrue, you don't get free money just because you want it.