Insure domestic Tranquility, provide for the common defence, promote the general Welfare.

According to the excerpt, the responsibility of government is to

Serve the people and protect them. the government should not harm or endanger the citizens.

According to these lines, the responsibility of government is:

Insure domestic Tranquility = Try to maintain peace among the citizens. Provide for the common defence = Protect the country against foreign threats. Promote the general Welfare = Ensure that the people of the country are happy, healthy and safe.