(CNN) -- House Republicans nervous about their prospects for keeping a majority may know soon after the polls start closing Tuesday night whether or not they've managed to pull a last-minute rabbit out of their political hat, in spite of the Iraq war, an unpopular president and a series of scandals.

The fates of 16 GOP incumbents facing tough races in a swath of states stretching from the Atlantic seaboard to the Ohio River Valley are likely to a bellwether for whether Democrats can shift the 15 seats they need to win control of the House for the first time since 1994.

In Kentucky and Indiana, where the last polls close at 7 p.m., Democrats have five Republican incumbents in their cross-hairs. In Ohio, where voting stops at 7:30 p.m., there are three more. And at 8 p.m., numbers will start rolling in Connecticut, where three moderate GOP lawmakers are trying to fend off challengers, and Pennsylvania, where five Republican-held seats are very much up for grabs.