US presidential hopefuls are to make final pitches to people in Iowa, where the first votes for party nominations will take place later on Monday.Polls suggest that Republican Donald Trump has a narrow lead over Ted Cruz but both are well ahead of the others, reports BBC.But the Democratic race is slightly tighter, with former US Secretary of State Hillary Clinton edging ahead of Vermont Senator Bernie Sanders.Each party`s nominee will contest the presidential election in November.Over the weekend, the candidates barnstormed the sparsely populated Midwestern state of Iowa in an attempt to court undecided voters.Campaigning is expected to continue until voting starts at 19:00 local time on Monday (01:00 GMT on Tuesday).Candidates are hoping to triumph in this first electoral test because victory can spark campaign momentum as voting moves to the other states.