The swirl doesn't come out too evenly from under the rim of the toilet seat so the cleansing action is not working as it should.
You may have calcium build up in the holes that direct these little jets of water.
Simply put a mirror in the toilet so you can see under the rim, and poke a coat hanger into each hole. That may unclog any clogged holes.
If the problem doesn't seem to be solved that easily, turn off the water and flush the tank. Then with some "plumbers putty" (found at all the plumbing parts counters) you can temporarily plug up all the holes by reaching into the bowl up under the rim. Then pour some CLR down the flapper hole in the tank. This will fill the rim of the toilet.
If you can keep the putty from leaking for a few hours, you can dissolve all the calcium build up and then flush it clean like a new toilet.