For the first six months of this year, the PS4 sold 1,592,000 units while the XBO sold 1,100,000 in the U.S according to NPD. That means the PS4 has outsold the XBO by 44.7%. Every month the PS4 outsells the XBO, the wider the numerical gap becomes and the harder it will be for the XBO to come out on top. Halo will provide a short-term boost at best, as individual titles rarely boost sales longer than a few weeks. The XBO could conceivably win in the months Halo 5 & 6 are released, but two monthly victories will be meaningless small victories in the sales war. The only thing that can stimulate sales on the long term is an actual price cut. If the XBO is reduced to $300 and Sony doesn't answer back with a price cut of their own, they stand a chance of closing the gap. However, I doubt Sony will go without a price cut of their own for long, plus I doubt MS will cut into the XBO's profitability so they aren't going to issue a price cut anytime soon. Maybe sometime next year, but not within the next few months. If the PS4 and XBO stay at price parity with each other for this whole generation, which is likely, then there is no conceivable stimulative factor that will propel the XBO ahead of the PS4.

Lost momentum is very hard to overcome, and it's extremely rare for a system that's trailing that far behind to mount a comeback and win. In fact, I don't think there's ever been an occasion where one system was starting off being outsold by its competitor by a 3:2 margin on average and was able to come back and win. The PS1 was trailing the N64 only slightly for the latter's first year on the market, but it took off like a rocket after FFVII came out, plus it already had a year's head start over the N64. The 360 edged out the Wii in the States, but it took it until 2013 to accomplish that task and it did so only because the Wii had weak legs, plus it's worth pointing out that the Wii and 360 were very different systems, whereas the only thing differentiating the PS4 and XBO are their exclusives, which amount to some 10% of their game libraries (the majority of the PS1 and N64 libraries were exclusives).

I'm sorry, but everything we know about the history of game sales in America suggests the odds of the XBO ever taking first place in lifetime sales or even consistently placing first in monthly sales are almost nil. There's always a slight chance, but if I were a gambling man I'd bet all my chips on Sony in this horse race. Had MS released a Kinect-less XBO SKU at launch, we might not be having this conversation, but waiting seven months to release it is too little, too late. But if it's any consolation, at least the XBO will do better here than any other region, and by time the final eighth-gen sales are tallied the PS4 might just barely obtain a majority, as opposed to the PS1 & PS2 which had 60+% supermajorities. I'm thinking a roughly 53%/35%/12% split for the PS4, XBO, and Wii U. Numerically, I think the XBO will likely land somewhere between the PS3 and NES in the U.S., which ain't half bad. It'd be second place, but a decent second place, and not what I'd call a "failure." Of course, Europe (sans UK) and Japan are already a lost cause for MS, and that's where it's going to hurt them.

Globally in the US?

This thread is about the US as it clearly states it in the title.

I edited that part out, I didn't mean globally as in all countries, I mean globally in the US (as in will have more total sales than the Ps4)