Most of the polling and election methods that report a percentage of the vote use the defective "vote for only one" Plurality Voting System. Whenever more than two candidates run, it unfairly favors the candidate most different from the others.
The fair voting systems can be coaxed to produce a "percent of the voters" figure, but the percents of all the candidates added together to a value more than 100%. This is because the fair systems let voters prefer more than one candidate.
Any newscast that gives percentages of the vote for candidates is getting these figures from polls using unfair methods. These polls match the election results only because the elections are also using the same unfair method.
More can be found at Unfair and Fair Elections: the Menu