The battle, in Republican Texas, pits Democratic congressman Robert Francis ‘Beto’ O’Rourke against Republican incumbent Ted Cruz in a state that hasn’t elected a Democrat to the US Senate for 30 years and which Cruz carried by 16 points in 2014.

While the focus is control of the 100-member senate, where 35 senators are up for election, voters will also be electing all 435 members of the House of Representatives, as well as 36 state governors and dozens of local legislative officials, in the November 6 elections.

Polls are showing the Texas race tightening. If O’Rourke does win, it will boost Democrats’ chances of winning the senate and would be a major defeat for US president Donald Trump and his party, which carried the state by more than one points over Democrat Hillary Clinton in the 2016 White House race.

Democrats will be hoping that these midterms will follow the pattern of most previous ones, in sending a negative message to the White House. But they must win seats in heavily Republican states such as Texas if they are to seize back the Senate. That’s why the party has much riding on O’Rourke, a fourth-generation Irish-American, who has already served two terms in the House of Representatives.

A number of leading Democrats have travelled to Texas to campaign with him. Among them has been Massachusetts Congressman Joe Kennedy, much to the delight of O’Rourke’s supporters, who are drawing parallels between their candidate and the progressive campaign of the late Senator Bobby Kennedy in the 1960s.

O’Rourke’s campaign is also being backed by some Irish-American political activists. Stella O’Leary, president of the Irish American Democrats lobby group, who knows the congressman well, says he actively engages on Irish issues, such as protecting the Good Friday Agreement and promoting trade between Ireland and the US.

“I was pleasantly surprised by the depth of his knowledge of Ireland,” O’Leary told me.

O’Rourke is the son of Melissa Martha Williams and Judge Pat Francis O’Rourke, whose forebears emigrated to Texas from Ireland in the 19th century to help build a railroad in the state. His father died in July 2001, at the age of 58, having been struck by a car while cycling.

He was nicknamed Beto, a common Spanish nickname for Robert. In a bizarre effort at denting O’Rourke’s popularity, the Cruz campaign has charged that he is using his nickname as a way of convincing Hispanic voters that he is one of them, when he’s really Irish. Cruz himself likes to embrace his own Irish ancestry — he is of Cuban, Irish, and Italian descent.

Huge crowds have been turning up for O’Rourke’s rallies and he has visited all of the state’s 254 counties. He has also shattered fundraising records, with a $38.1m haul between July and September, the largest quarterly amount in US Senate history and more than triple Cruz’s $12m. Nevertheless, Cruz has strengthened his position since Republicans won the contentious battle over Justice Brett Kavanaugh’s Supreme Court confirmation.

Some of his supporters say that a win by O’Rourke, 46, would catapult him onto the national stage, boosting fellow progressive Democrats, with him potentially making a bid for the Democratic nomination in the 2020 presidential race.

Indeed, the midterms are the unofficial start of the 2020 Democratic campaign for the presidency, with potential candidates, such as former vice-president Joe Biden and senators Cory Booker, Elizabeth Warren, and Kamala Harris hitting the campaign trail for midterm candidates, while testing their own messages and getting valuable face time with voters.

Trump, too, is focusing on 2020, while hitting the campaign trail. He calls Democrats “an angry mob” and said at a rally in Pennsylvania on October 10 that if they win a majority in Congress, they will destroy “the greatest revolution to ever take place in our country”.

Democrats have a strong chance of winning a majority in the House of Representatives. All of the 435 seats in that chamber are up for grabs and Democrats need a net gain of 23 to win control. Republicans now hold 237 of the 435 seats.

Notching up a majority in the Senate will be a far tougher battle. For a start, of the 100 seats in the Senate, where Republicans now hold a 51-49 majority, just 35 seats are up for grabs and, of these, Democrats are defending 26 seats, many in strongly Republican states, while Republicans have only nine to defend, none of which are in states that are strongly Democratic.

Ten Democratic senators are running for re-election in states that Trump carried in 2016. That alone should have all but guaranteed Republicans would add to their majority in the chamber, but polls are now showing that the tide may be turning for many of the Democrats, including senators Bob Casey of Pennsylvania, Sherrod Brown of Ohio, and Debbie Stabenow, of Michigan.

The most expensive Senate race is being fought in Florida, where Democrat senator Bill Nelson is trying to hold off a challenge from the state’s Republican governor, Rick Scott. Republicans have spent $66.3m so far, compared with $55.4m by Democrats, and, as the election enters the final stretch, that combined $121m is expected to increase significantly.

The Missouri race is among the tightest Senate contests in the nation. Democratic incumbent Claire McCaskill and her Republican challenger, Josh Hawley, the state’s attorney general, seem neck-and-neck. The RealClearPolitics polling average gives Hawley a statistically insignificant lead of less than half a percentage point, while the FiveThirtyEight site gives McCaskill a 56% chance of keeping her seat.

The most endangered Democratic incumbent appears to be senator Heidi Heitkamp of North Dakota. The RealClearPolitics polling average gives an almost nine-point lead to her opponent, while FiveThirtyEight suggests Cramer has more than a two-in-three chance of unseating her.

But it will be down to the party that can bring out the most voters, and turnouts in midterm elections is traditionally low. While 60% of Americans vote in presidential elections, only 40% take part in the midterms. And those who do tend to send a negative message to the party holding the White House. Over the past 21 midterm elections, the president’s party, be it Republican or Democrat, has lost an average 30 seats in the House and an average four seats in the Senate. Democrats may be glad Trump is in the White House.