Braun's lead is down to 5.9%. By the end, probably around 5%. Not a horrible margin for Donnelly, it's too bad he couldn't make up that last 5%.
If Donnelly wouldn't have promised to vote with Trump on immigration, it's likely he would have gotten higher turnout in East Chicago (known as "The Latino Gary" in Lake County) and Indianapolis, as well as among liberal youth and women.
Yeah, I remember seeing a news report of him saying he would consider voting with Trump on birthright citizenship. The second I saw that I figured he was done for.
He would've done worse other places, so it probably didn't make much of a difference.
Keep in mind this strategy actually used to work in the late 2000's. Bev Perdue ran radio ads in the last week about cracking down on illegals in 2008 Governor's race. McCrory was using it as a wedge issue to flip rural voters while trying to remain a Charlotte moderate otherwise (basically Romney style). It actually worked and Perdue held onto a lot of ancestral Democrats who voted for McCain over Obama, while McCrory ran 10% almost head of McCain in Mecklenburg County.
The reason why the strategy no longer works is because one of the two parties have firmed up the issue and thus the voters who care about this issue know who to vote for. Also Donnelly voted for the comprehensive bill in 2013, so he would have a tough time selling that line to these voters if they paid attention to it to begin with, which they probably did not because they have found their Presidential champion in Trump and Trump told them to vote for Braun, which they thus did.