The 14th Amendment was passed after the Constitution and its first 13 Amendments, so that it supersedes any provision of the earlier documents with which it might conflict, and modifies any related matter. That is what "amendment" means.
Because the 14th Amendment states, the "validity of the public debt of the United States, authorized by law....shall not be questioned", the country must pay its public debt. There is no discretion, no choice. Yes, it is Congress that has borrowing, taxing and spending powers, but the 14th Amendment's command that the country's obligations be paid makes it clear that those powers are not discretionary once an obligation has been authorized by law.
Analyzing this from the perspective of creditors, all holders of obligations by the United States government would have the right to sue to compel action if Congress does not do one of the following: a) raise revenues to pay those obligations; and/or b) lift the debt ceiling so we can borrow to pay those obligations; or c) pass a law canceling those obligations, so they are no longer authorized by law.
That is it. There is no room in the Constitution, as amended, for maintaining obligations but also not paying.
For example, suppose one held a US Treasury bond. If that bond is unpaid (or, arguably, when non-payment is sufficiently imminent), as an injured party, one should have standing to sue Congress to compel it to provide the funds and the authority to pay me. A properly informed Court would find that Congress may have the power to borrow money and raise taxes, but, that for obligations already authorized by law, it must exercise one or the other of both of those powers to meet those obligations.
Moreover, since the president has sworn an oath to "faithfully execute the laws" of the United States, he is also compelled by Constitutional language in the 14th Amendment to pay the country's duly-authorized obligations.
It is not discretionary, neither for Congress nor for the president. The Congress can determine the sources of those payments -- debt or revenue -- but it cannot leave the president without the means to pay.
Let us be very clear. Congress could not be compelled by a Court or an individual to establish Social Security or Medicare or rack up debt as it did under George W. Bush by reducing taxes, running wars, and providing a healthcare benefit and refusing to pay for any of it by matching those expenses with revenues. But, once Congress authorizes those obligations, and the president signs off, then, short of canceling those obligations, Congress has no discretion not to pay, and the President has no discretion to withhold payment.
If the Congress does not provide the necessary funding, through use of its powers, it is violating the oath of office. If the president does not pay the country's obligations, ditto for him.
One cannot brandish one's fealty to the Constitution and, at the same time, refuse to make the money available to pay our financial obligations. The latter is unconstitutional.
The Constitution, as amended, absolutely prohibits the United States from being a dead-beat nation. That seems like a pretty good idea.