Driver's side door latch

It was one of those days for my Riviera. My driver's side door is really hard to open. I pull the handle and it opens up about a half an inch and then stops. I then have to slip my fingers in the crack of the door and pull to get it open. Any suggestions on what I should look for. It was fine this morning, but when I got back to my car it was having this problem. The hinges look fine and there doesn't seem to be much up and down movement of the door. I think there might be some problem with the door latch. To add insult to injury, on my way home from work one of my headlights was burned out. It just wasn't her day.

Does it open smooth once you get it past that half inch?

Well I got it fixed. All I did was spray a little wd40 and it works better than before. I thought there was something wrong with the latch mechanism, so I am glad it was a cheap and easy fix. I know it will start to do it again once the wd40 goes away, so what is some good lubricant to use to keep it from sticking again? I guess it needed something after all of these years.

white lithium grease in spray can.