US public debt has crossed $40 trillion as its fiscal position worsens and Treasury yields move closer to levels that could threaten equities. Jefferies strategist Christopher Wood flagged a rise above 5% in the 10-year US Treasury yield as a key risk trigger, with the yield recently at 4.69%.

The federal debt reached $40 trillion as the government adds red ink at a rapid rate. That's leading nervous investors to demand higher interest rates —pushing up borrowing costs…

U.S. Treasury bond sell-off coincided with the nonpartisan Congressional Budget Office's release of statistics that the national debt is about to cross $40 trillion.