Voters in the eastern U.S. state of North Carolina are participating Tuesday in a special election for a U.S. Congress seat that is being closely watched by Democrats and Republicans for potential signs of the parties' prospects in next year's national elections.

Public opinion polls ahead of the voting indicated Republican Dan Bishop and Democrat Dan McCready running virtually even.

President Donald Trump and Vice President Mike Pence made last-second appeals in support of Bishop during visits to the state Monday.

The seat has been held by a Republican since the 1960s. The race has drawn so much attention and money for both candidates that it is the second most expensive special election for the House of Representatives in history.

McCready was the Democratic candidate during the 2018 election when he went up against then-Republican candidate Mark Harris. But the results of that vote were thrown out and a special election ordered after state officials ruled there was an absentee-ballot fraud scheme that benefited Harris.

Democrats made big gains in the 2018 election cycle and retook control of the House of Representatives. The entire House and about one-third of the U.S. Senate will be up for election when the nation also votes for president in 2020.