John McCain, the presumptive Republican nominee, has dramatically sliced into Democratic rival Barack Obama's lead in most nationwide polls, bringing the presidential race to a dead heat, according to dpa. An average of national polls showed Obama clinging to a 1.2 per cent lead - a statistical tie - in a tally provided by realclearpolitics.com, the closest margin in months and just days ahead of the Democratic convention in Denver, Colorado. Perhaps more telling, a realclearpolitics.com analysis showed McCain has taken the lead in the electoral college, the state-by- state breakdown that ultimately determines the winner of a presidential election. The analysis included polling in "toss up" states that can quickly swing the election, but for the time being gave McCain a slight 274- to-264 lead in the electoral count. McCain's jump on the Illinois senator came during the last week, while Obama was taking a break from the campaign trail and vacationing in Hawaii, and as the McCain campaign sharpened its attacks against Obama. The conflict between Georgia and Russia that erupted August 7 may have also been a factor. McCain made several tough statements criticizing Russia, a move that further strengthened voters' perceptions that he is more experienced and capable when it comes to foreign policy. McCain, 71, has also hammered Obama, 47, for his hardline stance against offshore oil drilling, with the Arizona senator striking a chord with voters unhappy about high petrol prices. McCain's attacks forced Obama to shift his position and back limited offshore drilling as part of his comprehensive plan to address the energy crisis. The Gallup poll, which tracks voter sentiment daily, showed Obama with a one-point lead on Tuesday before climbing back to two points on Wednesday. Obama can expect a boost in the coming days when he announces his vice presidential candidate and accepts the Democratic nomination August 28. Historically, presidential candidates experience a 5-per cent jump after the conventions. Obama's, however, could be short- lived because the Republicans begin their gathering September 1 in Minneapolis, Minnesota. Media attention has begun to focus on the vice presidential picks. Obama is expected to announce his running mate on Saturday in Springfield, Illinois, where he declared his candidacy. The Obama campaign has been carefully vetting the short list believed to include Delaware Senator Joseph Biden, the 66-year-old chairman of the Senate Foreign Relations Committee. Biden's experience on foreign policy could help Obama close the gap with McCain on the issue. Other candidates include: Evan Bayh, 52, a popular senator and former governor of Indiana; Bill Richardson, 60, the governor of New Mexico and; Tim Kaine, 50, the governor of Virginia. Hillary Clinton's name has also been thrown around, but Obama's chief rival for the Democratic presidential nomination is not considered a likely choice. McCain is believed to be considering Mitt Romney, the 61-year old former governor of Massachusetts who could help garner support for conservative Republicans sceptical of McCain. Other possible candidates are former Pennsylvania governor Tom Ridge, 62, and Connecticut Senator Joseph Lieberman, 66. Lieberman, once a Democrat and now an independent, openly supports McCain and the Republicans on most foreign policy issues.