Merz, the head of Germany's CDU/CSU conservative bloc, is in line to succeed Social Democratic Chancellor Olaf Scholz, whose fractious coalition with the Greens and the pro-business Free Democrats collapsed in November over contradictory plans to revive the nation's ailing economy.
Trump wants NATO member states to increase defense spending to five percent of GDP, at a time when Germany has only just reached the two percent mark for the first time.