To Democrats in Congress who have worked with Mr. Obama, the indifference conveyed to Mr. Reid, one of the president’s most indispensable supporters, was frustratingly familiar. In one sense, Mr. Obama’s response was a reminder of what made him such an appealing figure in the first place: his almost innate aversion to the partisan squabbles that have left Americans so jaded and disgruntled with their political system. But nearly six years into his term, with his popularity at the lowest of his presidency, Mr. Obama appears remarkably distant from his own party on Capitol Hill, with his long neglect of would-be allies catching up to him.

In interviews, nearly two dozen Democratic lawmakers and senior congressional aides suggested that Mr. Obama’s approach has left him with few loyalists to effectively manage the issues erupting abroad and at home and could imperil his efforts to leave a legacy in his final stretch in office.

Grumbling by lawmakers about a president is nothing unusual. But what is striking now is the way prominent Democrats’ views of Mr. Obama’s shortcomings are spilling out into public, and how resigned many seem that the relationship will never improve. In private meetings, Mr. Reid’s chief of staff, David Krone, has voiced regular dismay to lawmakers and top aides about White House operations and competency across a range of issues, according to several Democrats on Capitol Hill.