"What sort of lies" is pretty hand-wavy when it comes to labeling training data for a model. Are you summarizing from a source? I'm interested in the technical details of what happened.
Very few "undecided" voters truly are; elections are won and lost by getting your supporters to go to the polls. So if you wanted to use scurrilous, fake news to help your candidate, you'd be better off sending stories that will get your supporters really fired up and eager to vote and get their friends to vote, not trying to persuade the practically nonexistent undecided demographic.
Are you able to specify the sources based on which you are supporting these claims, namely that elections are not not decided by "undecided" voters but rather by pushing your supporters to the election polls?
The last piece has a short summary of the salient point:
> In fact, according to an analysis of voting patterns conducted by Michigan State University political scientist Corwin Smidt, those who identify as independents today are more stable in their support for one or the other party than were “strong partisans” back in the 1970s. According to Dan Hopkins, a professor of government at the University of Pennsylvania, “independents who lean toward the Democrats are less likely to back GOP candidates than are weak Democrats.”
> While most independents vote like partisans, on average they’re slightly more likely to just stay home in November. “Typically independents are less active and less engaged in politics than are strong partisans,” says Smidt.
> [...]
> The conventional wisdom holds that the parties need independents to win general elections, but the reality is that they’re increasingly devoting their resources to getting their own voters—including their “closet partisans”—out to the polls rather than trying to sway the dwindling number of genuine swing voters. “We’ve seen a huge increase in technology and the ability to turn out the vote,” says Smidt. “So in terms of a cost-benefit analysis, the parties and candidates see that it’s much easier to turn out people who agree with them than it is to change someone’s mind. And then there’s also the question of how many of us are even open to changing our minds.”
