WASHINGTON — Trump’s pick to be the Pentagon’s top civilian adviser, Elbridge Colby, vowed to provide the administration with “credible, realistic military options” to prevent Iran from obtaining nuclear weapons in front of the Senate’s Armed Services Committee on Tuesday, walking back his own previous arguments that the threat posed by a nuclear-armed Iran could be contained by the United States if it meant militarily defending Taiwan instead.

Under a withering barrage of questioning led by Sen. Tom Cotton (R-Ark.), Colby went so far as to say that a nuclear-armed Iran would pose an “existential threat" to the United States due to Tehran's development of space-launch rocket technology which experts say is similar to that needed to build intercontinental ballistic missiles. 

Colby, a former Pentagon policy official during the first Trump administration and grandson of US central intelligence director William Colby, has spent recent years riding the conservative talkshow circuit while arguing that the Pentagon should be uncompromising in prioritizing its military presence in east Asia to deter China from invading Taiwan. In his 2021 book, "The Strategy of Denial," Colby went so far as to assert that the US military should defend Taiwan even at the potential cost of allowing Iran obtaining nuclear weapon.

He appeared to renege on those arguments under intense scrutiny from Senate Republicans on Tuesday. In doing so, Colby fell squarely in line with Trump's revamped "maximum pressure" campaign, which US officials say is designed to coerce Iranian officials back to the negotiating table to re-impose limits on the country's nuclear enrichment program, after Trump's first presidential administration withdrew from the 2015 nuclear accord.