“What Trump is doing is un-American,” Schulz told the Funke media group. “The United States stand, like few other countries, for enlightenment, democracy and the values of freedom.”
In a stinging criticism of the US President, Schulz said that Trump was “running with a wrecking ball through American values.”
Schulz - up until mid-January the President of the European Parliament - was chosen on Sunday by the Social Democratic Party (SPD) to be their candidate to face Merkel in the national elections.
Since he has been named as candidate, the party have reached their best polling figures in two years.
The SPD man said that it is Berlin's duty to emphasize to Washington that Germany and Europe strongly oppose the policies of the Republican President.
Schulz's broadside on Trump was accompanied on Wednesday by that of another leading member of the SPD.
Justice Minister Heiko Maas told the Rheinische Post that “it is disturbing when people are being placed under blanket suspicion based on their beliefs or their place of origin.”
Condemnation of Trump, who has imposed temporary travel bans on citizens of seven Muslim-majority countries, while blocking Syrian refugees indefinitely from entering the US, has come from across the political spectrum in Germany.
On Monday, Merkel said that the travel bans smacked of anti-Muslim bias.
"The essential and also resolute fight against terrorism in no way justifies general suspicion against people of a specific faith, in this case people of the Muslim faith or people of a certain background," she told reporters in unprompted remarks.
"This approach in my view contradicts the basic tenets of international aid to refugees and international cooperation,"