President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE bears the blame for Democrats' electoral sweep on Tuesday, according to former Sen. Rick Santorum (R-Pa.), who said the president has failed to deliver the decisive legislative victories he promised.

"I think the bottom line is Donald Trump is not delivering on what he said he was going to deliver on, and that's the problem," Santorum said on CNN. "And he needs to deliver, and if there's a message for Republicans they better get that message and they better start passing stuff and looking like they can govern."

Santorum, who emerged as the runner-up for the GOP's presidential nomination in 2012 and briefly ran again in 2016, has generally defended and stood by Trump since endorsing him in May 2016.

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But a wave of Democratic victories — most notably in Virginia — has given the party a jolt of momentum heading into the 2018 midterm elections and signaled that Trump's deep unpopularity in his first year in office may be bad for Republicans looking to widen — or even hold — their majorities in Congress.

In the most closely watched race, Democrat Ralph Northam defeated Republican Ed Gillespie in Virginia's gubernatorial election. Trump took to Twitter shortly after the race was called to place blame on Gillespie for the loss, saying he failed to "embrace" the president during his campaign.

Santorum, however, rejected the notion that Gillespie was to blame. Democrats in the commonwealth were motivated to turn out, he said.

"It's not Ed's fault," Santorum said. "You're blaming it on Ed, and I just don't think it's Ed's fault."