Last year, a prominent group of supporters asked Hillary Clinton to address a prestigious St. Patrick's Day gathering at the University of Notre Dame, an invitation that previous presidential candidates had jumped on.

Barack Obama and Joseph R. Biden Jr. had each addressed the group, and former President Bill Clinton was eager for his wife to attend. But Mrs. Clinton's campaign refused, explaining to the organizers that white Catholics were not the audience she needed to spend time reaching out to.

As it became clear on Tuesday night that Mrs. Clinton would lose to Donald J. Trump, supporters cast blame on everything from the news media to the FBI director's dogged pursuit of Mrs. Clinton over her personal emails, and to a deep discomfort with electing a woman as president.

But as the dust settled, Democrats recognized two central problems of Mrs. Clinton's flawed candidacy: Her decades in Washington and the paid speeches she delivered to financial institutions left her unable to tap into the anti-establishment and anti-Wall Street rage.

Former Gov. Edward G. Rendell of Pennsylvania also said he had encouraged campaign aides at Mrs. Clinton's Brooklyn headquarters to spread their vast resources outside Philadelphia and Pittsburgh and focus on rural white pockets of the state. ''We had the resources to do both,'' Mr. Rendell said Wednesday. ''The campaign—and this was coming from Brooklyn—didn't want to do it.'' (Mr. Trump won Pennsylvania by 1 percentage point.)