Exit polls issued early on Monday showed Bolivia’s Socialists taking a seemingly insurmountable lead in the country’s bitterly fought presidential election, a result that, if confirmed by the official tally, would amount to a massive popular rebuke of the right-wing forces that drove the left from power a year ago. The exit poll by the firm Ciesmori, with margin of error of less than 2 percent, indicated that former finance minister Luis Arce had claimed 52.4 percent of the vote, compared to centrist former president Carlos Mesa’s 31.5 percent and right-wing nationalist Luis Camacho’s 14.1 percent. A second exit poll by a group of universities and Catholic institutions showed very similar figures, giving Arce 53 percent and Mesa 30.8 percent.