do you believe the u.s. would have defaulted on its debt, even if we never raised the debt ceiling?
I don't know for sure in the short-run, but the longer such a situation persisted, the more likely default would have grown. There was real risk or probability of debt default. It was not zero and over a sufficient period of time, such risk would almost certainly have grown more likely than not.
Some pundits and political leaders tried to suggest that there was essentially no risk. That's incorrect. Their benign scenario requires the following proposition:
Debt default would occur only when Revenue < Interest Payments for a sufficient time to deplete cash on hand.
The correct scenario includes both elements of debt service (maturing principal and interest). Under that approach, debt default would occur when Revenue < ∑ Maturing Principal and Interest Payments for a sufficient time to deplete cash on hand.
There was no assurance that this situation could have been avoided even under a prioritization of payments. If Treasury prices fell, interest yields would rise. As October 17 approached, short-term Treasury yields were rising, indicating waning demand for those securities. Shorter-duration Treasury securities need to be rolled over more quickly than long-term ones. Rising interest yields could further undermine demand for Treasury securities via changing risk perceptions, leading to further declines in Treasury prices and further increases in interest rates. A self-reinforcing cycle between falling Treasury prices and rising yields would trigger a situation where revenue eventually fell below the sum of maturing principal and interest payments wiping out cash on hand and, thereafter, producing a debt default. Moreover, even under prioritization, there would be a significant macroeconomic hit. That macroeconomic shock would reduce incoming tax revenue, further narrowing the Treasury's ability to ward off the risk of debt default.
There is no empirical evidence that the U.S. would somehow be immune to the kind of sequence of events that have culminated in other countries defaulting or being rescued from imminent default via the IMF and others. The U.S., of course, is of a scale that makes an IMF or international community rescue all but impractical. Certainly, the U.S. has not been immune to other financial crises (2008 providing the most recent example), so to assume that it would somehow be immune to a debt crisis is almost certainly unrealistic. Moreover, unlike with the Fed's extraordinary financial crisis interventions, the Fed really had no good cards to play. The Fed's stepping in to buy maturing Treasury securities to assure that they were rolled over would amount to the kind of large-scale debt monetization that has been behind currency crises in other countries (with significant macroeconomic consequences).
In short, no responsible Senator or Representative could deliberately risk such an outcome. The consequences of either a debt and/or currency crisis were too great. Those who voted against what is an imperfect deal, but one that avoided the finite but difficult-to-quantify risk of debt default or currency crisis were the Fed to have tried to step in, were deliberately risking that destructive outcome. That's extreme recklessness. It is not principled leadership by any stretch of the imagination.