"I consider it wrong that we should rapidly build up our military capacities following it. We should wait whether the United States really puts NATO into question. I think that this will not happen. And we should work to prevent it," Schulz told the German WDR broadcaster.
Schulz stressed that the issue should not "solely circulate around Trump," since the majority of US senators do not question the necessity of NATO.
In April, however, Trump noted that the United States would take steps toward enhancing NATO, adding that the alliance was not obsolete, which is contrary to the claim he made during his presidential campaign.
The comment followed a recent statement made by German Chancellor Angela Merkel about how Europe could no longer rely on its longstanding partners and should "take its fate into its own hands." The chancellors remarks were considered by some to be a reference to relations between Brussels and Washington.