By Molly Daly

PHILADELPHIA (CBS) — Word that President-elect Donald Trump is expected to nominate the CEO of ExxonMobil as secretary of state has lawmakers on both sides of the aisle concerned, given Rex Tillerson’s professional and personal ties to Russian president Vladimir Putin.

Senators Marco Rubio, John McCain, and Lindsey Graham have all voiced worries. Pennsylvania’s senior senator, democrat Bob Casey, weighed in on the news.

In response to KYW’s interview request, Pat Toomey’s staff said the Republican US senator was unavailable.

Senator Bob Casey says the concerns are significant, since a nominee for the job of top US diplomat usually has a long record of experience in foreign policy or government. Not so with ExxonMobil CEO Rex Tillerson.

“We’re talking about someone in the private sector representing a huge internationally dominant oil company, who has close ties to Vladimir Putin, who is on most days, an enemy of the United States of America. We work with him on some issues, but he’s pretty much a 24-hour bad guy,” said Casey.

Five years ago, Tillerson negotiated a multibillion dollar deal with the majority state-owned Russian oil giant, Rosneft. Putin attended the signing ceremony.

Casey says that, combined with the reported CIA finding that the Russian government interfered with the election to help Donald Trump win the White House, means a tough confirmation process.

“We’ll see how he answers these basic questions, on experience and knowledge, but also on these ties. I think there are a lot of concerns raised by people in both parties.”