While Rex Tillerson signaled his intention to be clear-eyed about Moscow, he refused to say whether he would back economic sanctions against Russia, and surprised senators at his confirmation hearing by revealing he has not yet discussed with Trump the incoming administration's position on Washington's former Cold War foe.
But during pointed questioning Tillerson said he believed it was "a fair assumption" that Russian President Vladimir Putin would have ordered his nation's meddling into the US presidential election.
The former ExxonMobil chief executive's remarks before the Senate Foreign Relations Committee came against a backdrop of controversy over US intelligence conclusions that Russia conducted election-related cyberattacks against US democratic institutions -- revelations he called "troubling."
"Russia today poses a danger, but it is not unpredictable in advancing its own interests."
Tillerson, whose entire professional career has been in the energy industry, has faced criticism for his business relations with Putin and other authoritarian leaders.
But the 64-year-old stressed that as Washington's top diplomat, he will conduct a more robust US foreign policy than during President Barack Obama's presidency.
To achieve 21st century stability, "American leadership must not only be renewed, it must be asserted," he said.
North Korea's closest ally, is seen as critical to containing Pyongyang's nuclear weapons program.
Tillerson, however, said disagreements with Beijing on some issues should not preclude "productive partnership" on other matters.
Former secretary of state Condoleezza Rice and secretary of defense Robert Gates -- Republicans whose consulting firm has worked for ExxonMobil -- recommended Tillerson to Trump.
And Trump, a billionaire businessman with property interests around the world, was impressed.
"The thing I like best about Rex Tillerson is that he has vast experience at dealing successfully with all types of foreign governments," Trump tweeted.
The Senate's Democratic minority will try to make life difficult for Trump's cabinet nominees.
Senator Ben Cardin warned Tillerson that operating an oil firm was far different than safeguarding American interests worldwide.
"Recent news accounts indicate Russia may well have information about Mr Trump and they could use that to compromise our presidency," Cardin said, alluding to a leaked dossier of unsubstantiated reports that claim Russia gathered compromising personal and professional details about Trump.
"It cannot be business as usual," Cardin insisted.
Some Republicans have also raised concerns about Tillerson.
If just three Republicans jump ship, his nomination could be blocked, despite support from party heavyweights.
Republican Senator Marco Rubio asked Tillerson if he believed Putin is a "war criminal" for the Russian military's attacks on Aleppo, Syria.
"I would not use that term," a steely Tillerson said.
When Rubio pressed him on whether Saudi Arabia was a human rights violator, Tillerson said he needed more information before making such a determination.
Until he stepped down from ExxonMobil on New Year's Eve, Tillerson was also director of Exxon Neftegas, an affiliate that operates the Sakhalin-1 field in Russia's Far East.
The US parent firm was chasing greater investments in Russia, including Arctic fields, and Tillerson was a familiar and popular figure in Moscow, awarded an Order of Friendship medal by Putin in 2013.
Tillerson was a staunch opponent of US and international sanctions against Russia for its aggressive behavior in Ukraine, where it annexed the Crimea region.
On Wednesday Tillerson would not say whether he would support fresh sanctions on Russia, suggesting that "by design" they could harm American business.
On the climate change front, Tillerson said he wanted the United States to remain "at the table" regarding international talks. Trump in the past has hinted at backing out of international climate agreements.