Borderline stars who became supporting actors -

It was thought that The Deer Hunter would propel Christopher Walken to the top. He starred in a film or two then settled into supporting roles.

Ralph Meeker might fit the bill.

Dennis Hopper?

I took "borderline stars" to mean they'd reached top-billing but then went down a few notches to supporting roles.

...a few to consider:

Sydney Greenstreet

Lawrence Tierney

Peter Lorre

Charles Bickford comes to mind. He began as a rugged leading man of the early talkie period, more or less along the lines of George Bancroft. He had a few good but unspectacular years, returned to the stage, then went back to Hollywood and soon found work as a strong characer actor. Bickford never lost his star quality. It's still there in The Big Country, in Days Of Wine And Roses.

Sterling Hayden's another like that, though he had a very different career. Hayden never liked or respected Hollywood, rather threw away his film career even after, thanks to the casting brilliance of John Huston, he reinvented himself as a tough guy in The Asphalt Jungle. A star in mostly minor A and program pictures in the Fifties he bounced back, after a few years absence, with his classic portrayal of Gen. Jacx D. Ripper in Stanley Kubrick's Cold War black comedy Dr. Strangelove.

Some interesting responses here.

There are a number of actors best remembered for being character players who had a shot at stardom, usually of the modest kind, who are best remembered for their character work. Lloyd Nolan comes to mind. He got top billing a few times early in his career, even had a short running B series in which he played Michael Shayne, Private Detective. But it's his character work that Nolan is remembered for,--and talk anout a scene stealer! He stole every scene he was in in Bataan!. Even in his clearly secondary role as the father of drug addict Don Murray in A Hatful Of Raine it's Nolan who feels like the emotional center of the movie. Why? Maybe it's because he seems most at ease in his part, doesn't appear to be trying so hard like his Methody (sic) co-players Murray and Tony Franciosa.

Arthur Kennedy had a few brushes with stardom, is remembered more for her sterling character work in films. On stage he was a name player; in films, a character actor. Van Herflin's career was similar. Like Kennedy, he got the occasional lead or secondary star billing,--Shane is a good instance of this--but he was seldom the main attraction. Early in her career Geraldine Fitzgerald showed the makings of a leading lady, but it never happened. She was, however, a superb actress, as her later character work shows. Shelley Winters, a star for a few years, if a minor one, became a major supporting player as she put on weight! Jane Alexander enjoyed a brief period as a sort of "star of tomorrow" before morphing into an accomplished character actress of great skill.

The actress who immediately came to mind for me when I read the topic was Tess Harper, but the more I think about it, maybe not because she's never been what I'd call borderline. It's more that I've seen her go from playing lead roles like in Tender Mercies to supporting roles, line in Crimes of the heart and No Country for old men and in various tv projects.