At the beginning of each legislative week, when most staffers are still cleaning out their inboxes or chatting about their weekends, Karen Haas is already looking at the floor schedule, trying to figure out when she’ll need to call in the “first string” House Republicans.

Those are the lawmakers who are regular fixtures on C-SPAN as they are most frequently tapped by Speaker Dennis Hastert (R-Ill.) to wield the gavel as Speaker Pro Tem.

“I kind of have a core group [of Members] that I go to for different things as well as appropriations bills,” said Haas, who has been a Hastert floor aide for five years. “The larger group is about a dozen, and there are probably six to eight that are first string that we go to a lot.”

The Members most often called to preside over complex or controversial legislation are Reps. Steven LaTourette (Ohio), Doc Hastings (Wash.), Mike Simpson (Idaho), Mac Thornberry (Texas) and Ray LaHood (Ill.).

The next tier includes Reps. Paul Gillmor (Ohio), Dave Camp (Mich.), Johnny Isakson (Ga.), John Shimkus (Ill.) and John Sweeney (N.Y.), among others.

While nearly every House GOP lawmaker has wielded the gavel at one time or another, Hastert and his staff believe those core Members are best equipped to handle tough floor debates judiciously.

“Any time someone’s dander is up we get a call,” LaTourette said.

Thornberry likened presiding over the House to “community service.”

“I think we are just the most gullible,” he joked.

Sweeney, meanwhile, suspects that he gets called when the leadership is in a bit of a hurry. “When we’re getting toward the end of the week, they like to have me there to keep the debate moving along,” he said.

Members may not preside over legislation that comes out of panels on which they serve. Simpson, LaHood and Sweeney, for example, may not handle Appropriations Committee bills.

Besides being fair, lawmakers who are handed Pro Tem duty are expected to have a good understanding of the chamber’s voluminous rules and traditions.

“I’m kind of a parliamentary freak,” confessed Simpson, who served for several years as Speaker of the Idaho House.

On occasion, that past experience will sow some confusion. Simpson recalled an incident when he was presiding in which a House Democrat made a floor speech and then ended it by making a motion to adjourn.

Simpson believed that a lawmaker is not allowed to end a speech with a nondebatable motion — leading to a brief argument between him and the parliamentary staff, who told him the motion was indeed permissible. After doing some research later, Simpson realized he was mixing up the House’s rules with those of the Idaho chamber, where such a motion would not have been allowed.

Like Simpson, most members of the “core group” have backgrounds that make them well-suited to the chair.

LaHood, a former aide to then-House Minority Leader Bob Michel (R-Ill.), is respected by Democrats and has been heavily involved in organizing bipartisan retreats. Thornberry is also a former House staffer, having worked for then-Reps. Tom Loeffler (R-Texas) and Larry Combest (R-Texas). LaTourette is a former prosecutor and brings his courtroom experience and legalistic knowledge to bear.

But none of that experience is really the same as serving as Speaker Pro Tem.

“When we took the majority, not one of our Members had ever sat in the chair,” said LaHood.

Most of all, each of the lawmakers has the appropriate reverence for the House and its sometimes unusual procedures.

“I really believe in the institution,” said Hastings. “I really do have a strong belief that you have open debate and the rights of the minority are respected and then you vote.”

Hastings presided over the record-setting three-hour Medicare vote Nov. 22 as well as the House’s passage of its version of the Medicare bill earlier this year. He was also in the chair when Rep. Bill Thomas (R-Calif.) made an emotional apology to his colleagues for calling the Capitol Police to clear Democrats out of a Ways and Means Committee room.

LaHood said “the most extraordinary” time for him as Speaker Pro Tem was Dec. 19, 1998, the day Rep. Bob Livingston (R-La.) announced he was resigning and called on President Bill Clinton to do the same. Just hours later, the House voted to impeach Clinton.

LaHood was also tapped to preside when Hastert announced the choice of Daniel Coughlin as House Chaplain after Democrats had leveled charges of anti-Catholic bias against Republican leaders. And on Sept. 11, 2001, LaHood was walking toward the House chamber to sit in the Speaker’s chair when a plane hit the Pentagon.

Through it all, LaHood has tried to stay focused on one goal. “A fair shake — that’s all people want when they come to the floor,” he said.

Sometimes, being fair simply means allowing lawmakers to keep talking, even if they go a few seconds over their allotted time.

“I try to let people complete their statements,” Simpson said.

Patience can also be a virtue, as it prevents the presider from issuing a ruling too hastily and then having to reverse him- or herself.

“You have to pause and wait for the Parliamentarian to whisper in your ear,” LaTourette said.

It’s not just experienced lawmakers who run the chamber. The Speaker’s office has asked each member of the GOP freshman class to handle special order duty for at least one week a year.

The first-term lawmakers who have most regularly wielded the gavel include Reps. John Kline (Minn.), Tim Murphy (Pa.), Marsha Blackburn (Tenn.) and Candice Miller (Mich.).

From the class of 2000, Reps. John Boozman (Ark.) and Rob Simmons (Conn.) have been particularly active.