Much better luck in OR and ID than in WA. That said, if you're going to a place that takes reservations, it's best to know the booking window and be on line when it opens up.
My most recent experience was up around Republic the week before Memorial Day. First come first serve forest service campground. I arrived on Monday and planned to leave on Fri before the weekend holiday crowd arrived. Well, the crowd started arriving on Tue and parked RVs and pitched tents in the available campsites and then just left even though the rules state you must stay in the campsite the first night you get it. Nope, these folks weren't doing that....they were essentially reserving a site for the weekend. Only saw one of them come back the entire five days I was there, and that was just to drop off a load of firewood. Kind of eliminates the first come first serve thing and pisses me off.
You guys do know we support all these criminals with "Snap benefits". That's food so they can spend their money on drugs to sell or use while they live in our playgrounds. They've got us by the short hairs, or we've given them our short hairs. If people were forced to support themselves and all they reproduce they'd act differently. They'd either get a job or end up in a crow bar hotel. Time we cut off the Snap support we provide! Let them make the choice of who they are and what they will contribute to society.
A lot of the "car camping" needs to have reservations a month or so in advanced for a weekend. However, if you get a wilderness permit for any of the national parks in the area, you can pretty much camp anywhere.