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One truism of presidential politics is that before any contender can clinch the Oval Office, they have to trounce everyone else in their own party. 

While former President Donald Trump will not be attending Wednesday's second Republican debate – which makes that hard for tonight's seven presidential candidates to do – they will need to take him out just the same, as well as each other, to get a shot at the presidency.

What remains to be seen is which of them might be capable of truly challenging Trump and not just feinting for attention, or looking for a post in his potential cabinet. 

Why does it matter? It could matter, because polls are showing widespread dissatisfaction among American voters over the advanced ages of the two presidential front-runners – Trump and President Biden, who are 77 and 80, respectively – and some polls are showing Republicans are still keen to find a viable Trump alternative, since the former president is facing 91 criminal indictments, which are likely to continuously threaten his candidacy.

Among those who will be debating tonight at the Ronald Reagan Presidential Foundation and Institute in Simi Valley, Calif., are Republican Florida Governor Ron DeSantis; former Republican South Carolina governor Nikki Haley; GOP candidate and entrepreneur Vivek Ramaswamy; former Republican New Jersey Governor Chris Christie; former U.S. Vice President Mike Pence; Republican South Carolina Senator Tim Scott; and Doug Burgum, Republican governor of North Dakota.

While many believed DeSantis might offer voters an appealing Trump off-ramp, his candidacy sputtered out of the gate and he continues to trail well behind the former president. 

As GOP hopefuls line up to debate Wednesday night, Haley is widely expected to attempt to nab the Trump runner-up position, as well as Ramaswamy. The big difference between the two is that Haley appears willing to swipe at Trump, whereas Ramaswamy has made it known he is a diehard Trump acolyte and would even pardon Trump if he won the presidency.

According to a recent memo from Haley's camp, the GOP debates still matter because around 60 percent of Republican caucus and GOP primary voters in early voting states have indicated they are actively looking to support a Republican candidate other than Trump. 

In addition, the number of voters fully committed to Trump in early voting states hovers at around just 25 percent, the memo says, which means there may still be wiggle room for a Trump runner-up to take the reins.

It may be a vanishingly narrow chance, but that's what most of Wednesday's presidential candidates are hoping for – even as the window rapidly closes.