If those buyers had a choice in the matter they would be foolish to buy treasuries.
The government has the power of force, however, and all of those 401(k) and IRA dollars will be buying treasuries with the "encouragement" of the US government.
The Argentine government pulled that one in 2008, seizing retirement accounts and placing miserably overpriced government paper in the accounts instead, with strong controls on withdrawals.
The Klintonx were involved with the election of the Menem Government that put in place all the ruinous fiscal policies that led to Argentina's financial blowdown in 2001, which was punctuated by the ignominious helicopter evacuation of a resigned president of the republic by helicopter from the Casa Rosada, the presidential palace -- shades of Saigon in 1975.
Democraps and Peronists think so much alike. That's why the Klintonx and their henchswarm were called "Clintonistas".