WASHINGTON (CNN) -- The two front-runners in the race for the Democratic presidential nomination rebuked Republican White House rival Rudy Giuliani on Wednesday for suggesting the United States could face another major terrorist attack if a Democrat is elected in 2008.

Barack Obama, an Illinois senator, said the man who served as New York mayor's during the Sept. 11, 2001, terrorist attacks should not be making the serious threat that faces the country into "the punchline of another political attack."

"Rudy Giuliani today has taken the politics of fear to a new low and I believe Americans are ready to reject those kind of politics," Obama said in a written statement. "'America's mayor' should know that when it comes to 9/11 and fighting terrorists, America is united. We know we can win this war based on shared purpose, not the same divisive politics that question your patriotism if you dare to question failed policies that have made us less secure."

Sen. Hillary Clinton -- without mentioning Giuliani's name, although an aide said the statement was responding to him -- said in a written statement that "politicalrhetoric" won't stop plots currently in the works against the United States.

"We have to protect our country from terrorism -- it shouldn't be a Democratic fight or a Republican fight," the New York senator said. "The plain truth is that this administration has done too little to protect our ports, make our mass transit safer, and protect our cities. They have isolated us in the world and have let al Qaeda regroup.

"The next president is going to be left with these problems and will have to do what it takes to make us safer and bring Democrats and Republicans together around this common mission of protecting our nation."