Reelection for Obama is far from certain at this point. He is not leading this race by 10 points. He is leading by 4. That is great for him, but that doesn't make him a winner in November yet.
If he is leading by 5 in two weeks (after the first debate and the September job numbers), it might be different.
That's what people said October 2008 when I suggested Obama start shifting resources downballot and nobody listened and Obama ended up getting 365 electoral votes, wasting a lot of EV's in the process and Democrats did far worse than anyone expected in the House. A campaign stop for Darcy Burner, Jim Esch, Bob Roggio, and Dan Seals would have made the Democratic victory complete that year. LBJ understood this in 1964 and put his money to use trying to get a huge House majority so that he could pass the Great Society programs.