What options are available to my Dad who is about $1000/month short the cost of AL? Do I have to cover the difference?

Another thing - your looking for AL for dad, right? If so find out if AL can be paid for by Medicaid in your state. Medicaid covers "skilled nursing care" aka a NH, but medicaid coverage to AL is done via a waiver program which can change (like my state, Louisiana is phasing out waiver funding and going to funding PACE) & a facility can decide whether or not to even take the waiver or does but limits the # of beds or decide not to continue participation with waivers.

It may be easier to get dad into a NH & onto NH medicaid from the start.

At 4K a mo, dad is going to have too much income for Medicaid. Most states have the ceiling for monthly income about $ 2,050. But all hope is not lost!, really.

What can be done for those who have just too much income for Medicaid is that they get a Miller Trust done aka A Qualified Income Trust. Miller in how it gets setup (and not a DIY project imho) needs to be done by an experienced elder law attny. The key in Miller is that the income has to meet being "qualified" most do but some pension plans are more iffy in guarantee so don't. Basically with a Miller all the monthly income goes into the Miller trust and then the individual gets paid by the trust whatever your state has as the maximum income allowed with the excess either building in the trust over time or paid to the facility. All the income reverts to the state upon death too. Really good legal will know how to make Miller work.

Also you may need to go to his MD's to get his chart built up to show the need for skilled nursing care. When they are living at home or in IL, they often do not flat have the fat medical chart that one coming from a hospitalization does do the Medicaid required "at - need medically" documentation.

There's going to be a lot of paperwork in all this. I'd suggest you go and get 2 cute binders (all the back to school stuff is in stores) and get one going for medical and the other for financial and start pulling his info together (like a yr of banking and his awards letters from SS and retirements) and schedule a NAELA attorney appointment. First one you can do without dad to get a review done on where he stands in all then, then next one dad goes with you.

One of the experts on this site - Gabriel Heiser - has a great book on the overview on the mice maze that is Medicare, Medicaid and elderly issues that is great. You can order it or find it in your library. Get the book & good luck.

Here is the website that is the portal to services in Washington state. You could find out if your father qualifies for Medicaid through them. In case AC deletes the link you can google washington connection org.
Washington Connection offers you a way to find and apply for a variety of services and assistance online. Click on “See if I qualify” to find out what services you may be eligible for through this site.
If you are:
Applying for children
A parent or caretaker applying with children
Pregnant or applying for someone who is pregnant
An adult 18 to 64 years old
You must apply for healthcare coverage at wahealthplanfinder org unless applying for help with Medicare expenses or with Long-Term Care services.
You can also contact your local Area Agency of Aging to see what's available in your area.

Babalou! Excellent suggestion! Poster, don't skip over that suggestion to negotiate. Babalou is so right.

Does dad have any other assets? If so, then start tapping those for the shortfall. Get in touch with Medicaid to begin that planning. Any other assets he had, though, would have to be spent on his care before they would step in. Gifting any assets away is not an option. I'm afraid there's no quick fix.

Does your dad have savings he could access to make up the shortfall?

I don't believe you should be shouldering the cost of your dad's AL rent unless you are very wealthy. You have your own retirement to think of. As to Medicsid, fist make sure that this is a facility that will accept Medicaid. You should talk to an certified eldercare attorney about qualifying for Medicaid.

You should also ask the facility if they are willing to take your dad at the full amount of his pension. The ALs in my area are always having "specials" and the stated price is often negotiable. I would look at several ALs, not just the least expensive one you think he can afford.