The race hasn’t started for many candidates since they haven’t yet announced an official campaign or began hiring staff around the country. However, there are a handful of GOP contenders who already have a serious ground game and are in the midst of building out a campaign network in the early states.

Report from Roll Call:

A veritable bevy of Republican presidential hopefuls have already hired staff, wooed deep-pocketed contributors and made speeches in Iowa and New Hampshire, proving what we already know: The 2016 nomination preseason is well underway.

Fundraising, organization, the size of the field and the calendar all will play a significant role in affecting how the race unfolds. The outcome is uncertain.

The current conventional wisdom is, in spite of changes intended to shorten the nominating process, the race for the GOP nomination could be more of a marathon than a sprint.

The last two Republican presidential nominating fights — with John McCain coming back from the political grave in 2008 and Santorum ending up as Romney’s final adversary — proved the race isn’t over until it is over, and that should encourage hopefuls to remain in the hunt even after their prospects have dimmed.

Still, not everyone who runs this cycle will have the wherewithal to remain a serious contender for the party’s nomination after the first couple of contests. Former Florida Gov. Jeb Bush and Kentucky Sen. Rand Paul are the two candidates who unquestionably have staying power.

Florida Sen. Marco Rubio and Wisconsin Gov. Scott Walker also likely will have the resources to wage serious campaigns during the nominating process, and they both have potential appeal to a wide swath of the party. That not only makes them intriguing contenders in the early nominating states, but also potentially interesting second choices to voters whose preferred candidates no longer are competitive.

Rubio is an excellent speaker with a compelling personal perspective, while Walker, a Midwest governor who took on and defeated the state’s public employee unions, has benefited from an early boomlet. They each have some appeal to both establishment and anti-establishment voters.

Louisiana Gov. Bobby Jindal, New Jersey Gov. Chris Christie, former Texas Gov. Rick Perry and Texas Sen. Ted Cruz must prove they can raise the resources to compete — not with Bush, who is widely expected to blow the rest of the field away when he reports first-quarter fundraising numbers, but with Rubio and Walker.

In terms of organization and financial backing, we’re seeing the actual candidate tiers emerge as the campaign announcements draw closer. Roll call breaks it down like this:

Top tier: Jeb Bush, Rand Paul
Mid tier: Scott Walker, Marco Rubio
Bottom tier: Cruz, Perry, Christie, Jindal, everyone else

The only one I disagree with there is leaving Ted Cruz in the bottom. Arguably, I’d say you could swap Cruz and Rubio since Cruz has deep Tea Party support which I think will give him some unforeseen strength in the early primary states. Then again, Roll Call is ranking them on organized support, such as campaign infrastructure, and ability to raise money at a competitive level, so maybe they’re correct on Rubio.

Rubio has bee cozying up to the Romney folks in recent weeks as an attempt to leverage Mitt’s fundraising network and stable of former campaign staff. It’s a smart move since Jeb has gobbled up most of what Rubio would ordinarily get in terms of support from Florida political circles.