When he was elected to the Senate, he was new to DC. When he was elected to the Presidency as a sitting US Senator, not so much.
1) You should not vote for someone with no experience in the the federal government, and
2) You should not vote for someone with experience in the federal government.
Of course, these are individually ridiculous criteria in electing a President, and even more ridiculous in combination.
Selecting a President requires more than verifying the presence or absence of a "past experience in federal government" line on a resume.