Willie Nelson’s tribute to the songwriter who famously called country music “three chords and the truth” is, like a lot of late-period Willie Nelson, a simple and undecorated album that reminds you how powerful simple, undecorated music can be. Though not quite as titanic an influence as Nelson himself (almost nobody is), Harlan Howard nevertheless gave us some of the most enduring and definitive songs in modern country, including “Streets of Baltimore” and “Tiger by the Tail,” both of which Nelson covers here. (He also wrote “I Fall to Pieces”; it’s not heard here, but its slightly jazzy lilt connected the dots between hillbilly music and rhythm & blues in ways that no doubt impacted Nelson’s own.) A traditionalist but never aggressive or posturing about it, Howard was one of those artists whose music you know but whose name you probably don’t. Nelson, who is on what is by some counts his 150th album, wants to make sure you do.