WASHINGTON — The White House's Islamic War coordinator to counter the Islamic State group was unable Wednesday to assuage Senate Democrats' concerns about what constitutes an "enduring" ground operation.

Senior Democratic Senate Foreign Relations Committee members pressed retired Gen. John Allen, special presidential envoy for the global coalition to defeat the Islamic State, about a section of a White House-crafted force-authorization measure that would "not authorize the use of the United States armed forces in enduring offensive ground combat operations."

At first, Allen did not provide even a notion of a specific definition. But when pressed by the committee's ranking Democrat, Sen. Robert Menendez, D-N.J., the retired Marine four-star, described the term broadly.

"Enduring might be two weeks, it might be two years," Allen told Menendez.

The answer did not sit well with some Democrats.

Sen. Barbara Boxer, D-Calif., told Allen his answer shows one thing about a definition of the White House's term. "There is none," she said.

"We're not very uncomfortable with this language," Boxer said, speaking for her Democratic colleagues.

Lawmakers from both parties say that the language might be too legally murky because, as committee Ranking Member Robert Menendez, D-N.J., put it, "the definition of what that is is problematic."

Sen. Edward Markey, D-Mass., noted he, as a House member, voted for the post-9/11 AUMF that two administration have used to legally justify US military operations in a number of countries. Markey raised concerns that the Obama administration's draft AUMF could allow this and future administration to also justify military operations beyond the countries for which it is immediately intended for over a decade.

The challenge lawmakers will have in crafting a war-authorization measure that can pass both chambers will be bridging largely partisan differences. Most Democrats view the White House's submission as too vague and broad, while many Republicans see it as putting too many limitations on this and future commanders in chief, as well as the military.

A picture shows two Russian S-400 Triumf S-400 Triumf missile system at the Russian Hmeimim military base in Latakia province, in the northwest of Syria, on December 16, 2015. Russia began its air war in Syria on September 30, conducting air strikes against a range of anti-regime armed groups including US-backed rebels and jihadist groups. Moscow has said it is fighting and other
A picture shows two Russian S-400 Triumf S-400 Triumf missile system at the Russian Hmeimim military base in Latakia province, in the northwest of Syria, on December 16, 2015. Russia began its air war in Syria on September 30, conducting air strikes against a range of anti-regime armed groups including US-backed rebels and jihadist groups. Moscow has said it is fighting and other "terrorist groups," but its campaign has come under fire by Western officials who accuse the Kremlin of seeking to prop up Syrian President Bashar al-Assad. / AFP / Paul GYPTEAU (Photo credit should read PAUL GYPTEAU/AFP/Getty Images)

For instance, committee Chairman Bob Corker, R-Tenn., for the second consecutive day asked whether the AUMF should include language authorizing US military strikes on Syrian President Bashar al-Assad's forces should they attack rebel forces there that have been trained and equipped by the United States.

Allen merely said he would have to "study" the question, but indicated he believes the US has an interest in seeing to it that those Syrian rebel forces are adequately defended.

Sen. Johnny Isakson, R-Ga., called the White House's draft AUMF "limiting" when compared to the one Congress passed after the Sept. 11, 2001, terrorist attacks. (Allen called it "limiting.)

Isakson told Allen he wants Washington to return to the period during which that 2001 authorization was approved, when he said US officials were willing to do anything necessary to fight terrorists.

Twitter:@bennettjohnt