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The final special election before the US midterms is currently too close to call, with Republican Troy Balderston just over 1700 votes ahead of Democrat Danny O'Connor in Ohio's 12th Congressional District. The Republican Party machinery converged on this suburban district for a furious eleventh-hour campaign aimed at saving a conservative House seat and averting a special election disaster.

President Donald Trump visited central Ohio at the weekend in hopes of boosting the Republican candidate. Trump won the 12th district by 11 percentage points in 2016 and it hasn't elected a Democrat to Congress since at least the early 1980s. A loss in Ohio, following shock Republican defeats in Pennsylvania and Alabama, would have further fed fears about a 'blue wave' in November's midterms. The narrow lead in such a previously safe conservative seat will do little to calm those fears.

An unknown number of provisional ballots are yet to be counted and Ohio law provides for an automatic recount if the two candidates are ultimately separated by less than half a percentage point. But whomever loses this week will get a rematch in the regularly scheduled election in just three months.