The New England Patriots are coming off of their sixth Super Bowl championship, but they are entering a 2019 campaign full of questions.

This is nothing new for the Patriots, as fans and media pundits always seem to question New England's roster heading into each new season, but this time around, there seem to be more legitimate concerns than previous years.

The Patriots have a lot of question marks at wide receiver, and with Rob Gronkowski gone, Tom Brady is now missing a pretty reliable security blanket.

Also, Brady himself is another year older, and you have to wonder at what point Father Time will finally begin to win out.

Still, the Patriots are the Patriots, and as a result, they are one of the favorites to win the Super Bowl going into this season.

Here are the three biggest X-factors for New England heading into 2019.

3. Michael Bennett

The Patriots lost their best pass rusher this offseason, as Trey Flowers signed with the Detroit Lions. New England replaced him by signing Michael Bennett, who spent the 2018 campaign with the Philadelphia Eagles.

Bennett totaled 34 tackles and nine sacks in a productive season this past year, but at 33 years old, there is a question as to whether or not he will be able to maintain that level of production this coming season.

Plus, Flowers was arguably the most dominant member of the Pats' front seven in 2018, so Bennett has some pretty big shoes to fill in replacing a young defensive end who just seemed to be entering his prime.

Michael Bennett, Patriots

The Patriots' defense was shaky for much of this past season, so hopefully for Bill Belichick, Bennett can provide a stable veteran presence without declining.

2. The Health of Demaryius Thomas

The Patriots signed Demaryius Thomas to try and shore up what has become a very thin receiving corps, but don't get too excited: this is not the same Demaryius Thomas from a few years ago.

Not only is Thomas now 31 years old, but he is coming off of a torn Achilles, an injury that is well-known to be debilitating.

Does he have anything left in the tank?

Brady may call Thomas' number quite a bit in 2019, as his only other options as far as wide receivers go are Julian Edelman, rookie N'Keal Harry, and Dontrelle Inman, who caught just 28 passes with the Indianapolis Colts in 2018.

If Thomas can somehow summon the strength to perform like he did in 2017 (at the least), he will be a boon to the Pats' offense.

Tom Brady, Patriots

1. Father Time

We keep hearing it over and over again when it comes to Brady, but one of these years, he is going to decline, because he is a human being, and human beings are mortal.

Brady will be 42 years old at the start of the regular season, and while he looked terrific in the Patriots' most recent Super Bowl run, the clock is ticking.

The future Hall of Famer showed some signs of a decline in the second half of the 2018 campaign, putting together some very concerning performances over the last couple of months of the regular season.

Was Brady just coasting, or was it a legitimate sign that he is getting closer to the end?

It remains to be seen just how long Brady can continue to fight off the inevitable.