April 28 (UPI) -- A wave of attacks in southwestern Colombia has transformed the country's presidential campaign into a debate over national security weeks before voters head to the polls on May 31. More than 30 attacks carried out between Friday and Saturday in the departments of Cauca and Valle del Cauca killed 21 people and wounded 56 others, renewing concerns over security guarantees ahead of the election. Paloma Valencia, a presidential candidate from the right-wing Centro Democrático,