WASHINGTON (CNN) -- Senate Republican Leader Mitch McConnell said he is "skeptical" about the Iraqi government but warned the recent U.S troop increase ordered by President Bush is the Iraqis' "last chance to step up and show they can be effective and can join with us to get this mission accomplished."

"This is it," he said.

McConnell's blunt assessment came the same day Senate Majority Leader Harry Reid, D-Nevada, announced that next Tuesday the Senate will take a key test vote on a resolution stating the troop increase is "against the national interest." The vote will determine if Reid can get support from at least 60 senators, the minimum needed to pass it.

Either way, Reid said the upcoming Senate debate will show that a bipartisan majority opposes the president’s policy.

McConnell, who supports the increase, said he also supports establishing benchmarks for the Iraqi government -- possibly as outlined in a resolution proposed this week by Sen. John McCain, R-Arizona, who also backs the troop increase. McConnell said benchmarks are the best way to determine if the Iraqis are holding up their end of the bargain but he stopped short of saying what the U.S. should do it the Iraqis fall short.

"I think everyone knows what the consequences are," McConnell said without specifying what he thinks they are, even when pressed.

"I'm not going to start playing out the scenarios," he added. "I'd just like the government in Baghdad to understand there is an overwhelming bipartisan desire for them to do what they need to do to make this mission a success."

But McConnell said the two resolutions opposing the new policy will send the wrong message. New coalition commander Lt. Gen. David Petraeus, who was confirmed by the Senate Friday morning, doesn't need the Senate to "micromanage the military challenge that he has ahead of him," McConnell argued.