Much more relevant is the cost of servicing the debt which has trended down/flat over time. Recent rising interest rates will change that somewhat but I see no real area of concern.
I see the opposite. Even if interest rates don’t rise more, we’re talking about a tripling of the service cost relative to GDP. That is going to put pressure on budgets for sure.
Where do you see a tripling? Are you mixing up the lines and their respective x-axis?
As you can see from the graph, the tripling of the debt ratio did not triple or even raise the service costs, because the debt market was absorbing debt for free or even at negative cost. The United States would have been very foolish indeed to have not borrowed under these terms.
The weighted average maturity of federal debt is less than 65 months and dropping. Only a very very small portion of the national debt is locked in for thirty years.