TL;DR: The way "we" talk about what the government or the taxpayers can "afford" and how we really do pay for things is wrong, government debt and deficit are neither intrinsically good or bad (though likely, to some degree, generally good!), inflation is the only real constraint on increasing government expenditure, the threat of inflation is exaggerated as it is actually easy to stop, mainstream beliefs about the level of the "natural" or minimum non-inflation causing level of unemployment are made up and almost certainly empirically wrong (too high), and all these things are essentially true if you are the United States of America in 2018, control the dollar printing machine, and all your debt is denominated in dollars.
I sort of ranked these in order of things that are close to being objectively true to things that liberals believe (which are probably also true!). The explicitly political element is that conservatives and the mainstream media which incorporates basically incorrect beliefs use deficit and inflation fears to implement their agendas. It is true that they hate inflation but they exaggerate these fears to make sure they win on the issue, and as we know, nobody really cares about the deficit.
