Surely you cannot be serious here. Europe is one (insert name)-exit away from total implosion. The Euro project was doomed from the very beginning: you cannot have a joint monetary policy without a unified fiscal policy (which never materialized through European consent - after failure of conquest i.e WW2)
The Euro area had a 2017 deficit of 0.9% of GDP, as compared to the U.S.'s 3.5%. And this is during a boom in the U.S.
https://ec.europa.eu/eurostat/documents/2995521/8824490/2-23...
The Euro isn't a better vehicle than the USD today, but it could easily become one. Not because the Euro improves but because USD will become less stable and attractive and the only realistic alternative is the Euro. Or maybe we end up with a more diversified system. Either way USD loses.
Get back to me when Saudi Arabia starts selling oil exclusively in Euros, or better yet, once European union surpasses the US in the number of aircraft carrier strike groups. You don't seem to understand the concept of a "foreign reserve currency" if you think Euro has a chance against USD. There is more chance of physical gold replacing USD as an inter-nation trade/reserve rather than Euro!
The U.S. is the world's reserve currency because everybody trades with the U.S. and the U.S. has run a current account deficit consistently since 1950, and with most of the world. That means everybody is holding USD and thus you can sell something to anybody else without needing sufficient imports from that buyer to cover the transaction. (Countries can't just buy USD willy-nilly; they need to find someone willing to trade USD for their local currency, which requires exporting some good or service.)
But that can change. Indeed, politicians are hell bent on changing it. And the global economy is exploding, meaning the U.S. won't be able to remain the center of the global commercial universe even if it wanted to.
Forget about the share of outstanding debt. That's money under the bridge. Think about the year-over-year change in the share of deficit spending funded by foreign buyers. Considering how explosive deficit spending will be over the next decade because of the tax cuts, compounded by higher interest rates, we could be in for a very bumpy ride.
What once were irrelevant swings in interest rates, current account deficits, domestic savings rates, etc, could quickly come to dominate the trajectory of the economy.
Sure, the Federal Reserve could soak up the deficit. But that would be much more likely lead to inflation than in previous periods.[1] Higher inflation means foreign buyers pull out, which leads to greater inflation and less capacity to purchase the imported goods that we're completely dependent on. It also means less profit on the international market for the high-margin services and industrial products we specialize in. Europe is doing a much better job than the U.S. at controlling deficit spending, and the Euro could easily become the new reserve currency.
[1] And don't forget, the Federal Reserve's mandate is low inflation and low unemployment. Congress may need to step in to change their mandate to de-prioritize low inflation, which would send a very nasty message to investors. Decades of easy money because of our current account deficit (aka trade imbalance) and strong domestic savings (via Social Security) has left people with a twisted perception of the consequences of budget deficits and inflationary monetary policy.