Trump has called on Nato's European allies to pay their fair share towards the cost of Europe's defence.
The Commission's proposal, published on Wednesday, consists of three possibilities: security and defence cooperation, shared security and defence and common defence and security.
They all provide for close cooperation between the EU and Nato, but vary in terms of voluntariness and obligations. In the next few months, the member states must decide whether and how to strengthen defence cooperation.
German MEP Michael Gahler, EPP group spokesperson on security and defence, said, "Irrespective of the approach which is eventually adopted, a common Union defence policy is foreseen in the Lisbon treaty. This requires a common responsibility for the protection of Europe and mutual support through cooperation among member states - without exceptions.
"The Commission's package adds value to the necessary member states' cooperation", said Gahler.
He added, "The European Commission's data is crystal clear: the lack of cooperation costs at least €25bn annually and the fragmentation of European defence is such that barely three per cent of European troops would be able to deploy if the need arose, despite the fact that collectively, European countries are the second largest military spenders in the world."
Because of the increasing threats and the worsening security situation in and around Europe, Gahler is sure that Europe needs to make its defence more efficient.
He said, "In times of Brexit and Donald Trump, the burden of improving European security lies primarily in European hands. We cannot only rely on others like we have done in the past. The European Union has to grow up and take care of itself, starting from now."
On Wednesday, the Commission also launched the European defence fund as well as a proposal for a regulation establishing the defence industrial development programme.
Gahler said, "Together, the three elements constitute a comprehensive package and an important step towards addressing the threats that we face. But now we need to achieve results. So let's start the countdown to a common European defence union. It is time for the EU and its member states to deliver on their commitments."