Image copyright Getty Images Image caption Biden said on Sunday he had made a secret trip to the US with O’Rourke
Democrat Beto O’Rourke has declined to invite vice-president Joe Biden to campaign with him in Texas.
Instead, the Democrat will hold events with Democratic presidential candidate Amy Klobuchar, to whom he introduced himself at a recent rally in Minneapolis.
Mr O’Rourke, a surprise election success in the state where Mr Biden is a veteran senator, is also expected to appear on Monday with fellow Texan Ted Cruz.
However, he is expected to file his US Senate term papers on Monday in Austin.
Texas is the biggest state in the US with 25m voters, but it is home to only 26 US senators.
Mr O’Rourke is seeking to replace Republican Ted Cruz, who is seeking a second term in the Senate.
The party is almost certain to retain the seat, but Mr O’Rourke’s success in the Democratic primary has made him a national attraction.
Some Democrats believe his grassroots campaign will make him a popular presidential contender in the 2020 election, should he wish to enter the race.
Mr O’Rourke has run a campaign as down to earth as he is energetic – dropping the same direct verb “we” through much of his campaign.
During the primaries he achieved what was thought impossible, winning a majority of the votes in Texas against an incumbent, nearly doing it in Chicago and going toe-to-toe with Republican incumbent Ted Cruz in the home stretch of the general election.