Despite the OP, which mentions only the IRA, I’ll also discuss the GRU.
In the case of the IRA, you would need to ask some campaign/advertising organizations to go through and do focus group testing and project results based on the targeting to try and get a real sense for it.
In general, I would probably predict that there was minimal effect. Their advertising budget was 1/200th of the GOP and the amount of sway that advertising actually has is fairly minimal. If it takes 200 units of money to shift people by 5%, then Russia would only be moving things by 0.025%.
That said, 0.025% of a population of 300,000,000 is 75,000 people. If you get them in the right place, that could swing things. Split over a few states, though, and that’s less useful. Russia didn’t target just one county or one state, they targeted a variety of regions, so that 75,000 is fairly dilute.
Also, the ads I have seen were all crazy nonsense. Crazy nonsense moves the opinion of crazy people and crazy people vote for crazy candidates.
The Russians spent some amount of their budget on Bernie and quite possibly did help him a fair ways since it’s not too hard to hook up crazies with crazies and the budgets in the primaries were smaller.
But in the main election, most of the crazies weren’t going to vote for Clinton anyways. She’s a fairly centrist candidate. Advertising to them, in this case, is sort of like working hard to convince programmers to eat pizza. You’ll certainly succeed but you’re not actually changing the needle.
To be fair, in the case of a razor thin margin, any minimal effect is important. But, the fact that there was already a razor thin margin means that it would already be fair enough for either person to win. And if you’re comparing a smart but crooked, centrist candidate to a stupid and crooked, crazy-wing candidate and seeing a razor thin margin than Russia isn’t the problem. There is some greater systemic issue.
Now, getting to the GRU, they probably had a significantly larger impact and quite plausibly did put things over.
They do seem to have given Stone targeting information, information from the DNC, and, plausibly, received back advice in some form. If you only have a budget of $1m, making sure that you’re not overlapping with the GOP is a big difference. This could have helped Russia’s IRA efforts to have been less dilute than they otherwise would have been.
More practically, knowing what the enemy was doing (i.e. Team Clinton) could be an immeasurable advantage.
Ultimately, you’re fighting for a handful of states that might switch over. Whether you win or not is predicate on your choosing which states to target and how much time to spend in those states. Once you know which ones your opponent is targeting, you can dump all of your advertising money into those ones, so there’s zero dilution, to spread a negative message while you figure out which states are good targets for you where you don’t have to compete head-to-head with the enemy. Clinton has to target every state in the country with an anti-Trump message, because she doesn’t know where he’s going.
If Trump had a budget of 200 and Clinton had 300, she’s at a first level advantage but, if he can target the 200 to five states and she has to cover fifteen, it’s really not a fair game.
Stealing information from the DNC is also important because there’s also the matter of the difference in budget between the campaigns and the budget of the mass media. The mass media has a larger budget than the campaigns by like 10X.
Everyone believes that Clinton is crooked. But they’re also liable to forget that matter unless it’s brought forward. So having news coming out that the DNC slashed Sanders’ tires brings a sort of immediacy and reality to the criminal-ish activities of Team Clinton. Here you suddenly have a billion dollars worth of free advertising going straight to the majority of the population. That takes a bite. Clinton’s turnout with younger voters almost certainly took a permanent nose dive because of that.
The GRU, it would be hard to argue otherwise, almost certainly had measurable and significant impact on the election.
In the next election, assuming that the Democrats elect someone reasonable, the Russians will be weakened by the lack of misbehavior on the part of the candidate going up against Trump. My guess would be that they’ll simply target Congressional candidates with an eye to boosting idiots and crazies. A stupid American government is, ultimately, the greatest advantage to Russia. Republican or Democrat is inconsequential.