Truthfully, combined with REAL spending cuts (not just reductions in annual increases), a wealth tax is the only way to start to get a handle on the national debt. That is, if we are serious about actually doing something about the debt. Where would that line be drawn, such as $10 million+, $5 million+, $3 million+ I don't know, but combined with real spending cuts it would be relatively easy to determine that mark. Well, that is based on the desired timetable, such as we want to retire the debt in 10 years, 20 years, whatever...
U.S. National Debt Clock : Real Time (usdebtclock.org)
Unfortunately the debt has grown so large, approaching $28 trillion, it would take some serious spending cuts, tax increases, and time, lots of time!