Under what administrations does the debt-to-GDP start rising? 

Pretty clear to me:

Figure 1: Federal debt held by public divided by GDP, %. NBER defined peak-to-trough recession dates shaded gray. Source: Treasury, GDP via FRED, NBER, author’s calculations.

There’s a party that’s loved debt over the past 40 odd years, despite protestations. Note also debt/GDP started rising precipitously in 2008Q3 (under G.W. Bush). It’s come down since 2021Q1, although rising in most recent quarters.

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