In August 1828, Justice Robert Trimble died just as President John Quincy Adams was battling a tough reelection campaign against Democrat Andrew Jackson. Adams ended up losing to Jackson, but in December nominated Kentucky lawyer John Crittenden to replace Trimble. (Recall that before passage of the 20th Amendment in 1933,  the presidential inauguration did not take place until March.)

Supporters of Jackson opposed this lame-duck nomination, leading to a debate of nine days on the floor of the Senate. Supporters of Adams's maneuver argued that it was a duty of the president to fill vacant slots, even in the waning days of a presidency. They offered an amendment on the floor:

    "That the duty of the Senate to confirm or reject the nominations of the President, is as imperative as his duty to nominate; that such has heretofore been the settled practice of the government; and that it is not now expedient or proper to alter it."

But this amendment was rejected in a voice vote and then the Senate voted 23-17 to adopt an amendment saying "that it is not expedient to act upon the nomination of John I. Crittenden." A few days after becoming president, Jackson nominated John McLean, the Postmaster General under Adams, to replace Trimble. (Jackson did this mainly to get McLean out of the Cabinet and to remove the possibility of him running for president, according to a study of the confirmation process.)

According to the Congressional Research Service, "By this action, the early Senate declined to endorse the principle that proper practice required it to consider and proceed to a final vote on every nomination."

It's matter of opinion whether a refusal to consider a nominee is a dereliction of constitutional duty or walking away from a constitutional responsibility. But the Senate majority can in effect do what it wants - unless it becomes politically uncomfortable. Democrats who suggest otherwise are simply telling supporters a politically convenient fairy tale.