U.S. Credit Rating

Two scenarios are possible although unlikely (and the second more unlikely than the first): a short delay in payment caused by technical difficulties with the debt ceiling; and an attempt by the current administration to restructure the US Treasury debt.

The question is about what a rating agency thinks, not markets. Well, they say what they think. Ratings agencies are there to forecast nominal default probabilities. US may choose to delay, restructure, etc. some debt. Has defaulted in the past.

technical defaults are possible

It's not the downgrade itself, but the fiscal conditions reflected in the downgrade. Debt to GDP is at a record high and growing fast, with barely a sign of fiscal discipline and some loss of foreign trust in US institutional strengths.

The US can always print money to make payments-so, payments will not be missed. But the printing will cause inflation – and this is the way to reduce the obligation. In 1971, when we went off the gold standard, many called this a default. Similarly, monetization is the key risk.

Measurable is a very weak hurdle, hard to see any positive news that makes the US a better creditor. Let's see if the world shrugs off Section 899 of the House Bill.
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The US debt to GDP ratio is high, forecasted to increase, and at the same time the US administration is explicitly considering aloud measures akin to default.

A substantial loss given default seems very unlikely (instead of inflating away the debt), but CDS spreads are substantial, which may reflect non-negligible probability of default (e.g. in debt ceiling event) and low price of cheapest-to-deliver security (30y issued in 2020)
-see background information here

Measurable. Not significant. But markets are forward looking, so it is already measurable.
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-see background information here
-see background information here

Is this time different? Possibly with the current budget proposal. Bigger concern is ability of treasury to place longer term debt and a spike in yields.