DLEWIS1941 - hi, look under the sink around the back area of the sink. You should see where that "stick" goes up and down. You'll see how it connects to the "plunger" and you'll probably see it's a type of clamp that's loose. You may need to replace the clamp, or you may be able to simply remove it, rebend it a little to get more tightness out of it, and then reinstall it.

For some reason, I'm drawing a blank on the names for the parts...you can check the Delta website and see a diagram of the parts, and find troubleshooting instructions as well. Also, one of the expert plumbers here may post a reply and give you easy to follow, clear directions. Good luck! Jim D/West Point, VA