美国总统选举初选即将在爱奥华州开始

After months of rallies, speeches and debates, the U.S. primary election campaign is set to formally get under way Monday, when Iowa residents cast their presidential preference at caucus sites across the Midwestern state.

Ahead of the crucial, first-in-the-nation 2016 vote, opinion polls in Iowa revealed a tantalizingly close race for both the Republican and Democratic Party nominations.

On the Republican side, real estate developer Donald Trump maintains a slight lead over Texas Senator Ted Cruz, who appears to have made several missteps in the lead-up to the Iowa caucuses.

For the Democrats, the race seems to be a virtual tie between former secretary of state Hillary Clinton and Vermont Senator Bernie Sanders, the self-declared democratic socialist.

Candidates in both parties made a final sprint through Iowa Sunday, holding events in every corner of the state, stepping up attacks on rivals and making last-minute appeals to key voter groups.