America’s budget deficit was already on an upward trajectory, thanks to an aging population and rising health costs. But it is now poised to take off.

After December’s sweeping tax cuts, which are expected to cut federal revenues by $1.5 trillion over ten years, the budget deal Trump signed Friday calls for an additional $300 billion in defense spending over two years.

The White House and lawmakers have also huddled over a $1.5 trillion plan to upgrade the nation’s infrastructure, with perhaps several hundred billion in taxpayer funds contributed in a possible public-private partnership.

Former President Barack Obama’s administration acted to reduce the deficit after the emergency spending in the wake of the 2008-2010 Great Recession, bringing it down from 9.8 percent of GDP in 2009 to 2.4 percent by 2015.

But having reached $666 billion in the 2017 fiscal year, it is on track to hit $1 trillion in…