The US is doomed to bankruptcy or default (according to an economics professor).

I recently watched The Great Course of economics professor Timothy Taylor, and read his book The Instant Economist. He keeps saying the US is doomed to bankruptcy or default. His reasons: 1. The US has enormously high debt. 2. People love to say we should cut the cost of government spending, but it's impossible, because most spending is uncuttable, like social security or Medicare. 3. Americans have a low savings rate, which means the government must borrow money from other countries. 4. Right now, most countries are happy to buy bonds from the US, but it's a trend that is impossible to sustain. At some point, they will slow down or stop. In the book and The Great Course, he said he failed to see how the US can keep raising debt, but he still failed to see how we can cut spending, which means the outcome must be bankruptcy or default. If that is the case, which bond ETF is the best? Definitely isn't BND. Maybe BNDW?