"The jury is out on whether the Trump election was the beginning of a new movement or whether it was a one-off election," Stewart told VICE News in an interview.
"Anticipating what the turnout is going to be in such a one-off election is extremely difficult, and that led to different assumptions by different pollsters," Podhorzer explained in a conference call with reporters on Wednesday.
By-elections are one-off elections in seats where, for example, the sitting MP has stood down or died.
"One" is the the number of years that have passed since the last presidential election, which technically makes 2013 an "off" election year.
Landrieu has fought off election scares before.
He returned himself to office in June after a violent one-man run-off election.
In April, one month before the run-off election, she hardened her approach, pledging to suspend all legal immigration to France in order to stop "this frenzy, this uncontrolled situation that is dragging us down".
In addition, unions draw on their political funds to provide one-off donations, mainly at election times, amounting to about £12m.
Debates have been held in Australia since 1984; in Canada regularly since 1979 after a one-off in 1968 and election debates are staged in most European countries.
If no one has achieved that number during the first round, then a run-off election will occur between two candidates who won the most votes.
So a run-off election is likely.
