The Constitution and 14th Amendment expressly list protecting citizens as a core responsibility of Government. However, a fetus is not a citizen until it is born. The IRS defines as US person as someone that is born.
Could the federal government argue that laws by states to protect the life of a non-citizen (a fetus) are unconstitutional according to a strict interpretation?
This does NOT imply that murdering a non-citizen should be legal as murder is a general law. States currently want new explicit laws for a fetus because they cannot try abortion as murder as they may like.
EDIT: The answer by bdb confuses the action of protection with a mandate of protection. This argument is not that protecting non-US citizens is unconstitutional. It is that laws mandating protection of non-US citizens are unconstitutional.