- he doesn’t have anything like a majority in the Argentine congress (in either house). I don’t know Argentine law and would welcome comments from someone who actually does but it would surprise me if this is something the president can do unilaterally.
- as a practical matter, Argentina itself does not have enough dollars to make this happen. You need a ton (more than that…) literally of physical currency to make this work. I don’t think their reserves are sufficient to cover it. (You need many additional tons of coins to make it practical too…)
Separately this is generally not a great idea economically. You do kill inflation in Argentina (replaced with American inflation but that is extremely low and stable by Argentine standards). But you have no control over your monetary policy or your exchange rates. If your economy is export driven to (e.g.) China, you now have to worry about the dollar-yuan rate, which is not under your control.
Of course this is also Argentina which is a particular basket case economically so I won’t rule out the possibility that this could be better than what they have now (or would have had under the loser in this election). But my guess is this would be worse if implemented.
For a country which produces a large number of really outstanding economists (including great macroeconomists!) Argentina is surprising disaster.