Cook potatoes in boiling water to cover 25 to 30 minutes or just until tender; drain and cool. Cut potatoes in half, and set aside.
Process vinegar and next 4 ingredients in a blender, stopping to scrape down sides. Turn blender on high, and gradually add oil in a slow, steady stream. Stir in chopped basil.
Place potato, tomatoes, and onion in a large bowl. Drizzle with dressing; toss gently. Cover and chill 8 hours. Top with crumbled bacon just before serving.
* 2 large tomatoes, seeded and chopped, may be substituted.