Opinions expressed in this piece are those of Joe Brettell and are not endorsed by ABC News.
The recent sparring between New Jersey Gov. Chris Christie and Kentucky Sen. Rand Paul displayed two potential contenders for the 2016 Republican nomination proving they could throw and take a punch. Christie has long been given the tacit stamp of approval from donors and party-wise men for a run at the Resolute desk, despite ruffling feathers with his embrace, both literal and physical, of President Obama shortly before Election Day 2012.
He is almost certain to run, and if he receives even a percentage of the financial support available to him in 2012, he'll be a formidable opponent.
The viability of Paul, however, has been a topic of mixed discussion around Washington. The junior senator from the Bluegrass State has certainly made an impact in his first term in the Senate, with crowd-pleasers like his marathon filibuster on privacy issues and willingness to engage both the media and majority party.
But it remains to be seen whether he'll be able to channel the grassroots energy that his father built, while simultaneously presenting his libertarian views in such a way that it can still be embraced by more moderate voters.
Moreover, Paul, 50, faces a taller task than his father, former Texas Rep. Ron Paul. In order to be viewed as viable in the run-up to 2016, he must display at least some measure of electoral coattails that will show voters and, more importantly, donors that he has some muscle.
That test will begin close to home, where Senate Minority Leader Mitch McConnell will be in a tough fight to retain his seat. Paul is heavily invested in the contest, with his former campaign manager running the McConnell campaign and Paul, himself, supporting McConnell in the race.
The results will largely be viewed by the political elite as a litmus test for Paul's strength in the state and his ability to rally his vaunted grassroots support into action.
Granted, some in the conservative movement who oppose McConnell will argue that Paul's willingness to support his colleague in an hour of need is a sign of "selling out." But a dose of political agility is something conventional Republicans will want to see before trusting him as a legitimate candidate.
Moreover, it's important to remember that the GOP nomination will be decided by delegates, not states, making voter enthusiasm and an ability to organize the grassroots vital to success. Few can argue the disruptive, often transformative effect that the Paul grassroots movement has had in the past several election cycles, affecting state conventions across the country in the most recent election.
With each election, Paul supporters have grown savvier about the process, causing headaches for many who often regarded state conventions as a mere formality
Political observers looking for early signs on whether a Paul candidacy might work should watch conventions in key states to determine whether his supporters will continue to surprise power brokers, or whether establishment Republicans have caught on to the game.