I think that there is an old Chines proverb that goes “every debt is eventually paid. If not by the borrower, then by the lender.”
All levels of government in the U.S. have foreign external debt and future unfunded liabilities of around $50 trillion. In this context, $1.0 trillion owed to each of Japan and China is manageable and the least of America's worries. Federal foreign external debt could be repaid in several years with increased Treasury bond sales to domestic lenders.
A future president should focus on the task of convincing Americans to live within their means.
Saudi Arabia is a different problem.