ABC News' Michael Falcone reports:

Kentucky Sen. Rand Paul, whose trip to Iowa this weekend is already stoking speculation about a potential 2016 presidential bid, is once again taking Hillary Clinton to task for her handling of last year's terrorist attacks in Libya.

In advance of his speech Friday night at an Iowa Republican Party gathering, Paul penned an Op-Ed in the Washington Times in which he writes that Clinton "should never hold high office again."

"My office is currently seeking out the witnesses and survivors of Benghazi to testify before the Senate Foreign Relations Committee. To date, the Obama administration has refused to let them testify. Too many questions remain unanswered. Now, there are too many new questions," Paul writes. "The evidence we had in January already suggested that Mrs. Clinton ignored repeated requests for more security in Benghazi. The new evidence we have today - and that continues to mount - suggests that at the very least, Mrs. Clinton should never hold high office again."

Paul's scathing critique comes days after State Department officials offered new details about the Obama administration's response to the Benghazi attack in testimony before the House Committee on Oversight and Government Reform.

Related: Benghazi Talking Points Underwent 12 Revisions, Scrubbed of Terror Reference

Paul, a member of the Senate's Foreign Relations and Homeland Security committees, plans to make Benghazi one of the major themes of his speech at the Iowa GOP's Lincoln Day Dinner Friday night in Cedar Rapids, Iowa, according to a source close to the senator. The source said the Kentucky senator and son of former congressman and presidential candidate Ron Paul, will also touch on immigration reform as well as the future of the Republican Party.

While in the Hawkeye State, a key stop on the 2016 circuit, Paul plans to meet with the Iowa Federation of Republican Women and attend a fundraiser for Iowa's Johnson County GOP.

Although other top Republicans, including Sen. Marco Rubio, R-Fla. and Sen. Lindsey Graham, R-S.C., also used this week's House Oversight Committee hearing to tear into Clinton, Paul's assessment stands out for its bluntness. And Republican outside groups have also seized the opportunity to take on Clinton, widely viewed as the Democratic Party's strongest potential 2016 hopeful.

On Friday the Karl Rove-backed super PAC, American Crossroads, unveiled a new video that Crossroads officials said highlights the "massive contradictions between the statements of former Secretary of State Hillary Clinton and others in the Obama Administration on the Benghazi attack." And it comes on the heels of another video released Thursday by America Rising, a new Republican opposition research group, which spliced some of Clinton's January congressional testimony on Benghazi with the testimony from Capitol Hill this week.