What is Turkish Air Miles & Smiles:
Turkish Air is a 1:1 partner of Capital One Miles & Citi Thank You Rewards. Turkish Air is based out of Istanbul, Turkey, and was ranked #17 among the top airlines in the world in 2021. By comparison, Delta, America's top-rated carrier on that list, sits at #30. With Turkish Air Miles & Smiles has a number of partners, United included, due to being part of Star Alliance, the biggest airline partnership in the world. Miles & Smiles is Turkish Air's frequent flyer program, and is usable on Turkish directly as well as their partners like United.
Image courtesy: https://flights.staralliance.com/en/members-codeshare
What's Possible:
In my opinion, while they can be a hassle to book (i.e. to book someone else, first you need to fly using miles yourself, then you need to call every time), Turkish Air has the best options for domestic long haul around, since you can regularly get 1 way domestic economy for 7500 points, or 12500 in business class, if you can find availability. That means you could book Maine (or in my case, Virginia) to Hawaii, Alaska, Puerto Rico, or the US Virgin Islands for those same fares.
Finding Availability:
To find availability for flights, go to the award calendar on United.com without signing in:
What you will be looking for is 12500 or less for a 1 way within the contiguous US (& sometimes a bit more than that if looking to book less than a month out), or 17500 or less if going from the contiguous US to Puerto Rico or the Virgin Islands, which can also be a bit more if looking less than a month out. Another option is Hawaii where saver fares should be between 22.5k-25k on United from distant locations like VA. Because things get difficult & complicated on rebooking via Turkish Air if the United flights are delayed or canceled on connecting itineraries, I recommend booking only direct flights unless you want to run the risk of encountering significant problems:
Image courtesy United.com
When you click on "Flexible Calendar" here is what that will look like:
Image courtesy United.com
If you'd really like to book around then, one option is to consider alternate airports to fly out of, with bigger airports tending to have higher availability. In my area in SE VA, Richmond (RIC) will tend to have more availability than Norfolk (ORF), and Raleigh (RDU), as well as Dulles (IAD), will tend to have more availability than those for anyone willing to drive a few hours (more if you hit DC traffic).
Image courtesy United.com
If you're flexible, you can look at other months until you find 17500. Some of the greatest availability is sometimes closer to when you are booking:
Image courtesy United.com
For flights <20k miles booked less than a month out that would typically be 17,500, look for it saving "Saver Award" after you click on it on the calendar:
Image courtesy United.com
Another option is Hawaii where saver fares should be between 22.5k-25k:
Image courtesy United.com