Voters can be excused for asking why so many people are still running for president when only three Democrats are consistently even registering better than 10% in the polls.

The answer is money. Thursday's debate was just the latest evidence of a shrewd game most of the remaining Democratic field is likely playing to boost or simply shore up their political cash lifelines.

While candidates can't pocket campaign donations for personal use, they can use funds raised for any campaign and transfer them to their efforts to another race at any time. Former Pennsylvania Gov. Ed Rendell cast more of a spotlight on that practice earlier this week in his Washington Post editorial pointing out how Elizabeth Warren has transferred some of her Senate campaign funds into the war chest for her presidential run.

But voters should be keeping a close eye on the money the presidential candidates raise that will eventually switch over to campaigns for something other than the presidency. This creates the lure of having a national spotlight, however fleeting, as a presidential candidate and the corresponding access to more and richer donors on a national scale.

The evidence is strong that this has been a central strategy for most of the Democrats running, or had been running for president this year. Former Colorado Gov. John Hickenlooper is out of the presidential running, but his candidacy helped boost his stature and his war chest for his new run for the U.S. Senate. Washington Gov. Jay Inslee is also out of the White House race, and now he also has more cash and more exposure ahead of his plans to run for reelection. In Inslee's case, many noticed that he was the only major candidate to accept support from a super PAC. One pro-Inslee super PAC netted millions from a tiny handful of wealthy donors.

But there is perhaps no better example of this trend than former Rep. Beto O'Rourke of Texas. He came into the 2020 race as someone most famous for two things: almost beating Republican U.S. Sen. Ted Cruz in 2018, and being very good at raising big money. The presidential race gave O'Rourke a chance to keep at least his fundraising prowess going. That's something that will help him enormously if he drops out and decides to challenge the other Texas Republican incumbent senator, John Cornyn. O'Rourke has strongly denied he'll do that, but many pundits still think it's the most likely scenario.

Running for statewide office in a giant state like Texas is an expensive proposition; one that forces potential candidates to face fundraising challenges similar to a presidential run. So why not raise those funds as a presidential candidate and keep a more logical connection to donors nationwide?

This strategy might also explain why Sen. Kamala Harris will remain in the race for some time. Even as an incumbent Democrat in a solid blue state like California, the size and cost of any statewide campaign in the Golden State is daunting. Harris now has much more money to spend on a likely reelection bid in 2022, especially if she continues to hold off on some spending in her presidential primary run. A recently obtained internal campaign memo noted how Harris hadn't made as many trips to New Hampshire as some of her strategists had wanted. Now, any decision that reduces travel costs starts to make more sense.