Rinse beans and soak them in plenty of cold water for 8 hours or overnight.
Drain and place the beans in a 4-quart saucepan with fresh cold water, covering them by an inch or more, along with the 4 bay leaves and 2 tablespoons oil.
Bring to a boil, partially cover the pot, and adjust the heat to maintain a bubbling simmer.
When the beans are almost tender, but still slightly undercooked, after about 40 minutes, remove from the heat; drain through a colander.
Stir in the 1/2 teaspoon salt and let cool; discard the bay leaves.
Add 4 tablespoons olive oil into the wide saucepan, scatter the bacon pieces into it, and set over med-high heat.
Cook, stirring, until the bacon starts rendering fat, then drop in the sausages; let them sizzle and begin to brown.
Add the chopped onion and the two bay leaves, and stir them around the pan bottom; meanwhile, keep rolling over the sausages so they color on all sides.
Cook for several minutes to allow the onion and meat to caramelize, then clear a space on the pan bottom and drop in the tomato paste.
Stir it in the clear spot for a minute, until sizzling, then spread the paste all around the pan, stirring and tumbling the sausages so they are coated.
Pour the red wine vinegar into a clear space in the pan, let it sizzle and evaporate for a few minutes, then stir and tumble everything again.
Pour 1 cup of hot water into the saucepan, increase the heat, and deglaze the caramelization as the water bubbles.
Pour in the crushed tomatoes and stir well.
Rinse the tomato containers with a second cup of water, and pour that in too.
Season with 1/2 teaspoon salt, stir everything together, and bring to a boil.
Keep the tomato sauce bubbling gently for about 10 minutes, then spill the beans into the pan; stir in the beans while the sauce returns to a boil.
Stir in the water, if needed, so the sauce is loose and nearly covers the sausages and beans.
Cook at a gentle boil, stirring now and then, until the beans are tender and the sauce has nicely thickened, 10 minutes or more (add water if the beans need longer cooking; or, if the sauce seems too loose, reduce it quickly over high heat).
Turn off the heat, and adjust the seasonings with salt and pepper.
Cover the pan to keep the beans warm until the polenta is ready to serve.
Assemble individual portions in warm wide pasta bowls; first dip a large spoon in water, and with it scoop up polenta and mound it in each bowl.
Spoon over a generous helping of beans in sauce, and lay a sausage on top.
Drizzle with olive oil, grind on more black pepper, and serve immediately.