From what I'm reading if may have some positive effect on voter share and possibly a negative effect on voter turnout. And that positive messages have have a positive effect on turnout. Isn't that the claim meme?

And, historically, Democrats win with greater turnout. At least as far as I'm aware.

Disclaimer: I've only spent 20 minutes on this. A properly measured response would take longer.

References

How Much Do Campaign Ads Matter?

The researchers found that, in the 2000 election, allowing only positive ads would have increased overall voter turnout from 50.4 percent to 52.4 percent. Meanwhile, airing only negative ads would have decreased turnout to 48.8 percent. The gap between the all-positive and all-negative scenarios was about 10 million voters.

“That’s pretty big,” Gordon says. “It does suggest that negative ads might have a detrimental effect” on election participation.

The Effects of Negative Political Campaigns: A Meta-Analytic Reassessment

This 2007 meta analysis is the most recent meta analysis I could find. It throws into question both claims, that negative ad have a positive effect on voter and negative effect on turnout. There's been a lot of studies since then, but this still gets cited.

The conventional wisdom about negative political campaigning holds that it works, i.e., it has the consequences its practitioners intend. Many observers also fear that negative campaigning has unintended but detrimental effects on the political system itself. An earlier meta-analytic assessment of the relevant literature found no reliable evidence for these claims, but since then the research literature has more than doubled in size and has greatly improved in quality. We reexamine this literature and find that the major conclusions from the earlier meta-analysis still hold. All told, the research literature does not bear out the idea that negative campaigning is an effective means of winning votes, even though it tends to be more memorable and stimulate knowledge about the campaign. Nor is there any reliable evidence that negative campaigning depresses voter turnout, though it does slightly lower feelings of political efficacy, trust in government, and possibly overall public mood.

Positive Spillovers from Negative Campaigning

Negative advertising is frequent in electoral campaigns, despite its ambiguous effectiveness: Negativity may reduce voters' evaluation of the targeted politician but may have a backlash effect for the attacker. We study the effect of negative advertising in electoral races with more than two candidates with a large‐scale field experiment during an electoral campaign for mayor in Italy and a survey experiment in a fictitious mayoral campaign. In our field experiment, we find a strong, positive spillover effect on the third main candidate (neither the target nor the attacker). This effect is confirmed in our survey experiment, which creates a controlled environment with no ideological components or strategic voting. The negative ad has no impact on the targeted incumbent, has a sizable backlash effect on the attacker, and largely benefits the idle candidate. The attacker is perceived as less cooperative, less likely to lead a successful government, and more ideologically extreme.