The Democrat has energized young voters with his optimism and charisma, forcing his opponent to pull out all the stops

Beto O’Rourke’s insurgent Democratic campaign to steal a US Senate seat in Texas from the Republicans for the first time in a quarter of a century entered its final hours with the party’s new superstar showing no let-up in his legendary energy levels or momentum.

The Texas Senate race is not only the most closely watched of any senatorial contest, given O’Rourke’s audacious bid to eject Ted Cruz from a seat that until this year was assumed to be rock-solid Republican. It has also become the most expensive US Senate race in history – passing the $100m mark.

It is a sign of O’Rourke’s exceptional appeal among young liberals not just in his home state but across the country that $70m of that massive sum was raised by him, most of it through more than a million modest online donations. Cruz’s relatively lackluster fundraising of $30m has forced him to seek logistical support in the infrastructure of Greg Abbott, the powerful governor of Texas, and the local Republican party.

But given conservatives’ vastly superior political machine in Texas, together with the fact that every statewide elected post has been filled by Republicans since 1998, this battle remains Cruz’s to lose. Polls have given him a lead of up to six points, but the gap has been tightening in recent days to within the margin of error.

'Beautiful Ted': Trump and Cruz bury the hatchet as midterm anxiety mounts Read more

Faced with an unexpectedly threatening opponent, Cruz has been forced to call in the cavalry in the form of his erstwhile enemy from 2016, Donald Trump, who staged a Make America Great Again rally in Houston last month. But even with Trump’s backing, Cruz has still struggled to get his message across in the face of O’Rourke’s optimism and charisma.

The contrast was on display on Monday when the two rivals made competing stump appearances in Houston, the largest city in Texas, which will play no small part in determining the outcome of the election. Cruz barely managed to attract 175 supporters to a Baptist church in a Houston suburb, while according to the Dallas Morning News, O’Rourke pulled twice that number to a barbecue restaurant in town.

Facebook Twitter Pinterest Beto O’Rourke’s efforts forced Ted Cruz to call in Donald Trump for support. Photograph: POOL/Reuters

What makes this race so unpredictable is the astonishing turnout in early voting that is the product of passions running historically high among voters on both sides of the political divide. Almost 5 million Texans have already cast ballots at polling stations or through the mail – more than double the rate of the last midterm elections in 2014.

That, combined with a record 1.6 million newly registered voters added to the rolls over the past four years, has left O’Rourke confident that he is starting to make inroads into communities that lean Democratic but traditionally tend not to vote at all. That includes two of his core target constituencies – young Texans and Hispanic voters.

Beto O’Rourke v Ted Cruz: debate heats up in Texas Senate race Read more

O’Rourke’s team has been especially encouraged that within the enormous early voting turnout, almost 8% of the tally came from newly registered voters. “These are the new voters,” O’Rourke advisers told followers on Monday. “They are hundreds of thousands of people who normally don’t show up in midterm elections – who are going to win this race for Beto.”

Play Video 10:26 'Those horrible pink hats': midterms divide women in era of #MeToo – video

El Paso, a border town situated in the dry, far western corner of the state separated by the border from the Mexican city of Juarez, itself displays signs of hope for its most famous resident. Almost 140,000 people have already cast their votes – an extraordinary number in a city of only 690,000.

The early voting turnout in El Paso is almost twice the total number of votes cast in the city in 2014. If enthusiasm continues into election day, almost as many ballots are likely to be cast in total as in the presidential race two years ago.

That would meet one of O’Rourke’s most fundamental objectives: to arouse such engagement in this midterm election year that it matches a presidential election. By doing so, he hopes to drive to the polling stations new and sporadic voters who have for so long been unheard, yet who have the potential to change the face of Texas.