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If you want to feel involved: Join a city or state-level campaign (cold calls, knocking on doors, publicity events, etc).

If you want to be involved: Run for a local office (like maybe a city council seat), preferably an uncontested race where a write-in campaign can be effective with minimal ad spending.

If you want to learn: Join the local chapter for a national campaign. Try to get yourself nominated as a delegate.

If you want to cause a specific impact: Be wealthy and donate significant amounts of money to causes you care about.