WASHINGTON — As President Trump weighs potential gun safety legislation, his attorney general on Wednesday floated a plan to expand background checks for gun buyers, but the idea was met with skepticism from key Republicans and appeared to face serious obstacles on Capitol Hill.

The proposal being circulated by Attorney General William P. Barr is similar to the so-called Manchin-Toomey bill, which would extend the current background checks system to all commercial gun sales, including those at gun shows and online. That bill fell to a Senate filibuster in 2013.

The White House made clear that the Barr proposal — which senators described as an “ideas list” or a work in progress — has not yet received Mr. Trump’s blessing, further underscoring the degree to which bipartisan talks around gun safety could fail. Mr. Barr, speaking to reporters in the Capitol, also played it down, saying he was “just kicking around some ideas” to see what could gain traction in the Senate.

Mr. Trump, for his part, took to Twitter on Wednesday in what appeared to be a proactive effort to lay blame on Democrats should the bipartisan talks fail. He singled out Beto O’Rourke of Texas, a former congressman and current 2020 Democratic presidential candidate, who has proposed a mandatory government program to buy back assault weapons — an idea that makes even some Democrats skittish.