For one thing, it staunched rising momentum for Clinton, causing enough concern that she largely shelved plans to adopt a more positive message in the campaign's close in favor of continued attack on her rival.
Mook said on GMA on Monday, 'I don't think Donald Trump dashing around to these states at the last hour is going to do what is needed to get his supporters out'.
Pennsylvania: The final Morning Call/Muhlenberg College poll found Clinton with a four-point lead in a four-way match-up. "The American people are sick and exhausted of hearing about your damn emails", Sanders said.
In recent national polling averages, Clinton leads head-to-head match-ups against Trump, with the Democrat holding 46.8 percent support compared to 44.3 percent for the NY businessman, according to averages compiled by RealClear Politics.
Trump jolted the first Republican debate in August 2015 when he was the sole candidate among 10 men on the stage to raise his hand to signal he wouldn't pledge to support the eventual GOP nominee.
For this to happen, Trump will also need core Democratic voters to stay at home, as well. In only one state did the polls miss the margin by more than 3 points. But not in the closing days of the contest.
Imagine, for instance, the first meeting between the Federal Bureau of Investigation director and the president-elect, whichever candidate wins.
Clinton has called in the stars - Barack and Michelle Obama, Jay-Z and Beyonce, Joe Biden and Bernie Sanders and Jon Bon Jovi have campaigned for her. Trump has only his kids and a few failed gods of the Republican Party for help.
Do African-American voters show up? "My faith in our future has never been stronger", Clinton told supporters.
If the answer is no, it could hobble Clinton in key states - particularly Florida and North Carolina. Among those with less education, almost six in 10 likely voters, it's 43-48 percent, Clinton-Trump.
Just a couple blocks away near the Lincoln Tunnel, the Clinton campaign will host the "Hillary for America Election Night Event" inside the Javits Center. Still, a sizable share, 42 percent, mainly oppose Trump. "Both he and Michelle have been awesome on the campaign trail", Clinton said at an election rally in Philadelphia yesterday.
While the large white working-class populations have put OH and Iowa in Mr Trump's column, they could yet swing back.
"I know there's a lot of frustration, even anger, in this election season", said Clinton, but anger is not a plan.
One of the most striking elements of the campaign has been both candidates' consistent unpopularity -- the highest on record for major-party candidates in ABC/Post polling back to 1984 and in Gallup polling (to the extent comparable) since the 1940s.
Rami Brown, 28, has voted for Mrs Clinton because he can not imagine himself voting for Mr Trump.
Trump had planned to keep up his breakneck travel schedule deep into Election Day, but aides revised plans, keeping the businessman in NY.
And Trump, in particular, has cast the election as rigged - calling into question whether ballots that are mailed in will be counted, playing up inaccurate reports of voter irregularities and claiming that voter fraud is pervasive.
Will the eventual loser legitimize the victor?