We all saw it just a few years ago. USC was back and ready to compete for a national championship with a Heisman candidate senior quarterback in 2012.

But it wasn't to be...

The Trojans dropped their Pac-12 opener to Stanford, underwhelmed in a soft early conference schedule and then dropped five of their final six including an embarrassing loss in the Sun Bowl. When the dust cleared in El Paso, the Trojans finished 7-6 despite entering the season ranked first in the nation, Lane Kiffin was pretty much a lame duck and it looked like it would be at least a few more years before USC became a national contender again.

Those few years have gone quickly and now the Trojans are looking like a preseason Top 10 and Playoff contender in Steve Sarkisian's second year. Things are starting to get exciting again in Trojanland, but with the stench of disappointment from 2012 still around, I can't help but think about some ways that could end making the Trojans underwhelm again.

The Sark Factor

Steve Sarkisian has more than proven himself as a good recruiter and a solid coach in the Pac-12, but huge questions remain about if he is the kind of elite coach that can get a team to completely maximize its potential. This could be a coming of age season for Sark, but his lack of history showing adjustments and taking a team to the next level leave me a little bit wary of the Trojans even winning the Pac-12 South.

Lack of proven playmakers at receiver

There is a ton of buzz about sophomore Juju Smith turning into the next Robert Woods/Marqise Lee/Nelson Agholor, but who else is there for Kessler to throw to? Developing star cornerback Adoree Jackson will likely help, but other than him, there are no proven playmakers at receiver. The leading returning receiver after Smith is Darreus Rogers who had less than 250 yards receiving in 2014.

Tight end will be a potential problem area as well with emerging standout Bryce Dixon leaving the program during the off-season. Dixon's absence leaves the Trojans without a tight end that has ever caught a pass.

I have a hard time imagining a team competing for a national championship in this era without the talent and depth at receiver to rip off points at will.

Schedule

The Trojans don't have an easy path to the Playoffs. A mid-season trip to South Bend to play a borderline Notre Dame team piles onto a difficult Pac-12 slate. Most difficult will be the final two weeks of the season where the Trojans have to travel to Eugene in the second to last week of the season and then follow up  with their rivalry game against a very good UCLA team. On top of that, say USC wins the South, they almost assuredly will then have to play Oregon again in the Pac-12 Championship Game. If that happens, a three week stretch with a game against UCLA sandwiched by travel games against Oregon sounds like a nightmare.

Depth

The sanction depth situation is just about over, but it is still there. The Trojans may be solid with their starters at just about every position, but they are very thin at a lot of positions just after the starters. They still can't afford to suffer injuries in 2015.

Big game experience

This is more about if the Trojans do manage to keep themselves in the Playoff chase late into the season. You usually see it where a team needs a prior year at elite level, playing in national pulse games to get themselves accustomed to playing at their best on the biggest stage. The Trojans have played some big games in their careers, but I don't think they are as battle tested as teams like Ohio State, Alabama and Oregon are right now if they lock horns in marquee games.