The way I usually hear the debt issue described these days is that it's ultimately a matter of ratios. If the deficit isn't too bad, debt payments are reasonable, and there is a certain amount of growth (making assumptions on that last one can be risky), then there isn't really much incentive to pay off debt instead of using that money for better things. On the other hand, if the amount of money it takes to service existing debts grows too large, then a situation can develop where either the government is choked by debt servicing or prints money out the wazoo to pay for it, devaluing the currency with the various consequences that entails.
As I understand it, the U.S. has been pretty lucky post-Recession in the Obama years in that even though our debt has spiked, due to the safe reputation of U.S. bonds and the like the cost of our debt servicing hasn't spiked nearly as badly. Of course, CBO has been predicting that interest rates and the cost of our debt servicing ought to go up any time now, so the Trump administration may get caught paying the price for the debts Obama undertook.
(I do think that Obama was right to undertake such debts in the face of the recession, and the hated 'sequester' has served a decent purpose, but neither party has been willing to take a hard look at the main deficit drivers - discretionary spending isn't really the main problem these days. EPA's budget, for example, is not even one half of one tenth of one percent of our spending.)
From what I've heard, though, Trump hopes to take control of the Fed and use monetary policy for political ends. If that ends up true things may get a bit topsy-turvy.