Trump tests strength of the Republican brand

(CNN)One of the big questions we'll be parsing after Election Day is the strength of the Republican brand in the age of Donald Trump.

Several weeks ago, it looked like Trump was inflicting serious damage on the GOP. But then the race tightened and is a nail-biter in the final hours.
We'll be looking for answers about the future of the Republican Party in the results of the down-ballot races -- particularly the races that will determine control of the Senate. Will some of those establishment candidates who distanced themselves from Trump survive in states where Trump gets trounced by Hillary Clinton?
    One reason we may see more split ticket voting this year is because many of those Senate candidates have been running strong campaigns in their states, independently from their presidential nominee.
    There's also been a fascinating political experiment playing out in battleground states across the country by third party groups that are not supporting Trump.
    Activists for Americans for Prosperity, the grassroots organizing arm of the Koch brothers network (as well as the well-staffed teams of those Republican Senate candidates) have been trying for months to convince conservative voters to get to the polls even if they can't stand Trump.
    Unlike 2012, when AFP spent more than $33.5 million against Barack Obama, AFP opted out of the presidential race this time. They focused their efforts on eight states: Ohio, Pennsylvania, Indiana, North Carolina, Missouri, Nevada, Florida, Wisconsin and one US House race in the outskirts of Denver.
    Trump's lift or drag on the Republican congressional candidates will be different in each state.
    Trump could pull out a win in Pennsylvania. But if Trump loses the state by four or five points, allies of incumbent Sen. Pat Toomey believe he can survive. If Trump loses by six, seven or eight points, they believe that's too much of drag on the ticket to eke out a Republican victory.
    Republican pollster Whit Ayres says, so far, voters seem to be distinguishing between the Trump brand and the Republican brand. That is evident because candidates like Rob Portman in Ohio, Chuck Grassley in Iowa, Marco Rubio in Florida and John McCain in Arizona are running significantly ahead of Trump.
    "Data is showing that a lot of voters are deciding on down-ballot races based on their own evaluation of the candidates or the job performance of the office holder - and that's occurring quite independently of their evaluation of Donald Trump," Ayres said.
    Even if they lose the White House, that trend could be a good sign for Republicans as they begin rebuilding their party.