@gideontax in general resourcing of US income that is also taxed by a foreign taxing authority is possible for all countries that US has a tax treaty with. Obviously if you want to use Portugal as your home, then yes Portugal has a tax treaty with US.
Note that while US would recognize 100% of the taxes paid to a foreign taxing authority, the allowable amount for the current tax year is limited on form 1116 -- lower of what you have paid or the US tax liability allocated to this doubly taxed income..
On Roth or similar tax advantaged income , I have to go refresh my knowledge on US-Portugal Tax treaty for specifics, but in general if an amount is taxed by the Foreign Taxing Authority as " income", then it is eligible for Foreign Tax Credit treatment ( again depending on exact facts and circumstances ).
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