Organizers took pains to ensure the trip goes smoothly.
"Helms is a Southern gentleman, but he's also a straight-shooter and often tells it as it is," Peschard-Sverdrup said. "And that sometimes can be perceived as not being diplomatic."
"This trip is being very highly choreographed and scripted to make sure that this is a historic moment, and that there are no unfortunate incidents or misquotes that end up undermining the significance of this trip," he added.
The trip is the latest in exchanges between high-level officials of the two countries since the elections of Fox and President Bush, the former Republican governor of Texas.
In February, Bush made Mexico his first diplomatic stop after his inauguration. Just two days later, a delegation from the congressional Hispanic caucus flew south to meet with Fox and other high-level officials.
Mexican foreign minister Jorge Castañeda Gutman, and Minister of the Interior Santiago Creel met with Secretary of State Colin Powell and Attorney General John Ashcroft just two weeks ago. Adolfo Aguilar Zinser, Mexico's national security adviser, left Washington last week. Ashcroft said he plans to visit Mexico soon.
In addition to meeting with Fox and the Mexican Senate foreign relations committee, the American senators were expected to meet with Castañeda, Attorney General Rafael Macedo de la Concha and Secretary of the Economy Luis Ernesto Derbez.
On Friday, the heads of state of 34 countries in the Western hemisphere — including Bush and Fox — will meet at the Summit of the Americas in Quebec City, Canada. Cuba is the only country in the region that will not be attending the summit.
On Wednesday, the United Nations Human Rights Commission will vote on whether to condemn Cuba for its human rights violations. Robert S. Leiken, senior fellow at the Brookings Institute, said that at last count, the projected vote was tied on whether to censure the country.
Mexico has traditionally shared close ties with Cuba and abstained from censure votes in tacit support of Fidel Castro. But Leiken said Mexico's new government feels less tolerant of Cuba.
"Now the issue is whether Mexico is going to condemn Cuba or abstain" and not the other way around, Leiken said.
Andrew Selee, coordinator of the Mexico project at the Woodrow Wilson Center, said there is a shift among Mexicans on both the political left and right on how Mexico should treat Cuba.
"You see for the first time some very vocal groups saying the Mexican government needs to support Cuba, but also condemn Cuba on human rights," he said.
The U.S. senators are scheduled to return to Washington on Wednesday evening.