At the National Constitution Center in Philadelphia on Tuesday, President Biden decried Republican efforts to limit ballot access across the country as a "21st century Jim Crow assault," while warning Americans that the GOP push to restrict voting and a "selfish" challenge of the 2020 election results were "the most significant test of our democracy since the Civil War."  Biden also hinted at future administration action on voting rights, saying that he and Vice President Kamala Harris "will be making it clear that there is real peril in making raw power, rather than the idea of liberty, the centerpiece of the common life."  But while he was encouraging more Americans to participate in the political process, Biden stopped short of endorsing changes to the Senate filibuster rule that would allow Democrats to pass voting rights measures with a simple majority vote, something advocates -- as well as many Democrats -- have begged him to support.  That did not go unnoticed by voting advocacy group, Black Voters Matter.  In a statement released after the president's speech, the group criticized the Biden administration as “acting as if its hands are tied" when, it said,  that isn't strictly the case. "In fact, the President didn’t mention the filibuster once in his twenty-minute remarks, despite the massive threat it poses to voting rights and other key legislation."