Chris Christie is one of the GOP's brightest stars and one of its best hopes for 2016. But during his toughest hour, he simply hasn't been able to count on a chorus of national GOP support rallying full-bore to his side.

(Mel Evans/Associated Press) (Mel Evans/Associated Press)

But why? Three reasons: The fluidity of the 2016 Republican field for president, continued uncertainty about "Bridge-gate" and the lack of a vocal/visible national base in Christie's corner.

Let's take a look at each one, beginning with 2016. Christie is seen as one of the front-runners -- if not the front-runner -- for his party's nomination. for president. But there are a host of other elected officials who may run, too. Officials like like Sen. Marco Rubio (R-Fla.), one of the prominent Republicans who has kept his powder dry regarding Christie.

"I think this is a story that's still developing and we should reserve judgment," Rubio said on CBS's "Face the Nation."

Wisconsin Gov. Scott Walker (R), another potential 2016 candidate, adopted a similarly noncommittal tone last week.

"Chris is someone I’ve worked with, a valued colleague. I don’t know enough about that situation to know what the impact’ll be,” Walker told a local affiliate.

Sen. John McCain (R-Ariz.), whose presidential ambitions are behind him, adopted an uncertain tone, even as he praised Christie's response to the episode.

"Is this a blow to him? Obviously," McCain said Sunday on CNN's "State of the Union." "How permanent it is, I think we will know in the days and weeks ahead."

The reality is that as 2016 takes shape, potential candidates -- and allies of those would-be candidates -- need to be very careful what they say. Praise of one hopeful could be portrayed later on as tacit support for that person, or even viewed as affront to an opponent. (Yes, we're as shocked as you are that politics can be so petty and personal). So praising Christie now as he takes heat over a traffic scandal -- unless you are absolutely going to be in the Christie camp come 2016 -- is not a risk-free proposition.

What's more, there is uncertainty about the scandal itself. And a cardinal rule of politics is this: Know exactly what you are supporting or opposing before you do it.

If the scandal -- which now is limited to former Christie aides and appointees, not the governor himself -- goes much deeper than what we've already seen, it would be a bad news for Christie. But it would also be bad political news for those who vouched for him. Tethering oneself to an uncertain situation is a perilous political decision.

Christie's rise in GOP circles is in no small part due to an invisible but immensely powerful donor and power broker class that loves him. This wing of the party tried to woo him to run for president in 2012, even after Mitt Romney was in the race. And they are expected to be there for him in large part come 2016, should he make a national bid.

For the most part, these are not the folks who are on the front lines of the media battle, making cable news appearances and staging press conferences. Karl Rove, who has defended Christie, is part of this group of behind the scenes players. But his forward-leaning public profile the exception to the rule.

Others have also rallied to Christie's side. Republican National Committee Chairman Reince Priebus vouched for him Sunday. So did former New York City Mayor Rudy Giuliani (R).

But Priebus is a hard partisan, and it's his job to defend his party's leading figures. And Giuliani is no longer in elected office, affording him more leeway in what he says than other Republicans.

Some Republican governors including Terry Branstad of Iowa, Susana Martinez of New Mexico and Nikki Haley of South Carolina have also voiced support for Christie in some capacity. As GOP governors, they are more natural allies of Christie. And all of them are up for reelection in 2014. Christie is the chairman of the Republican Governors Association, which spends money in governor's races. In short, it wouldn't be the wisest political move for any of them to alienate themselves from him right now.

One more thing to keep in mind: Christie is not beloved by the conservative base, which has been skeptical of him on various fronts as he's risen to national stardom. And some conservatives doubled down on that skepticism when the Bridge-gate scandal broke last week.

It's not that the party has abandoned Christie. Not by a long shot. just It's that a full-throated, wide-ranging net of support isn't there when he needs it most.

Sometimes the view from the top can indeed be very lonely.

Updated at 2:17 p.m.