President Trump may not be running for reelection yet himself, but the days and weeks before the 2018 midterms have been busy for him nonetheless.

On Thursday night, Trump appeared in Missoula, Mont., to stump for Senate candidate Matt Rosendale and incumbent Rep. Greg Gianforte running for re-election; on Friday he went to Mesa, Ariz., for Senate candidate Martha McSally; and on Monday he’ll be in Houston for Sen. Ted Cruz. There’s no question that the rallies are drawing crowds — the Houston event had to be moved to a bigger venue — but whether they actually make a difference will have to wait till Election Day to be seen.

That said, enough people think it works that it’s considered normal for a sitting President to campaign for congressional candidates during midterms season. But that wasn’t always the case — and when Presidents do get involved, it doesn’t always help.