PLANO, Texas — Facing the toughest race of his Senate career, John Cornyn warned a small crowd of supporters from the second floor of his campaign bus last week that his party’s long-held dominance in this historically ruby-red state was at risk.
But while the three-term Texas senator demonized Democrats at length, he didn’t spend much time talking up the obvious alternative: President Trump, the leader of his party, the man at the top of his ticket on Tuesday.
Asked whether Mr. Trump, the man who redefined Republicanism, was an asset to Mr. Cornyn’s re-election effort, the senator was suddenly short on words.
“Absolutely,” he said, stone-faced.
Mr. Cornyn’s gentle distancing from Mr. Trump foreshadows a far less genteel battle to come. This year’s election seems likely to plunge both Republicans and Democrats into a period of disarray no matter who wins the White House. With moderates and progressives poised to battle each other on the left, and an array of forces looking to chart a post-Trump future on the right (be it in 2021 or in four years), both parties appear destined for an ideological wilderness in the months ahead as each tries to sort out its identities and priorities.
The questions facing partisans on both sides are sweeping, and remain largely unresolved despite more than a year of a tumultuous presidential campaign. After Democrats cast their eyes backward several generations for a more moderate nominee, does a rising liberal wing represent their future? And what becomes of a Republican Party that has been redefined by the president’s populist approach, and politicians like Mr. Cornyn who have been in the long shadow of Mr. Trump for four years?
Traditionally, presidential elections provide clarity on how a party sees its political future. When Barack Obama won the White House in 2008, he reinvigorated a progressive public image of his increasingly diverse party. Eight years earlier, George W. Bush remade Republicanism with a message of “compassionate conservatism.”
Today, with both presidential candidates content to make the race a referendum on Mr. Trump, questions about him have overshadowed the debates raging within both parties over how to govern a country in the midst of a national crisis.
“Both sides have been content to make this election about a personality,” said Brad Todd, a Republican strategist and an author of a book about the conservative populist coalition that fueled Mr. Trump’s victory in 2016. “Therefore, we’ve not had a lot of light shown on the ideological realignment that’s occurred in the country.”
The jockeying has already begun. If Mr. Biden wins, progressive Democrats are preparing to break their election-season truce, laying plans to push for liberals in key government posts, including Senator Elizabeth Warren of Massachusetts as Treasury secretary. If Mr. Biden loses, progressives will argue that he failed to embrace a liberal enough platform.
Ambitious Republicans, like the former United Nations ambassador Nikki R. Haley, Secretary of State Mike Pompeo and Senator Tom Cotton of Arkansas, have begun appearing in Iowa, stops that they say are on behalf of their party’s embattled Senate candidate there but that have distinctly 2024 overtones.
“The party is headed toward a reckoning, whatever happens in November, because you still have large segments of the party establishment that are not at all reconciled with the president’s victory in 2016,” said Senator Josh Hawley, Republican of Missouri, who is frequently mentioned as a possible 2024 contender. “These people are still very powerful in the Republican Party, and I think we’ll have a real fight for the future.”
The emerging dynamics are particularly stark across in Texas and other states in the Sun Belt, a fast-growing region that embodies the demographic trends that will eventually reshape the nation.
For Republicans like Mr. Cornyn, the battle lines are already being drawn. Four years ago, Mr. Trump mounted a hostile takeover of the Republican Party, winning the support of the party’s base with a message that shredded mainstream conservative ideology on issues like fiscal responsibility, foreign policy and trade.
A contingent of the party’s old guard is eager to cast the president as an aberration, a detour into nationalism, populism and conspiracy theories with no serious policy underpinning.
Former Senator Jeff Flake, Republican of Arizona, said that he expected Mr. Trump to lose and that he hoped the defeat would refocus the party from “anger and resentment” to developing an inclusive message that could win in an increasingly diverse country.
“Nothing focuses the mind like a big election loss,” said Mr. Flake, who was one of many Republicans to retire in 2018 and who has endorsed Mr. Biden for president. “The bigger the better when it comes to the president.”
He added, “Trumpism is a demographic cul-de-sac.”
Mr. Flake would like the party to resurrect its 2012 “autopsy,” an assessment commissioned by the Republican National Committee to explore why the party had lost its bid for the White House that year. The report urged the party to better embrace voters of color and women.
A co-chair of the project, Ari Fleischer, said there was no returning to the days of that message. Mr. Trump, he said, had accomplished the goal of the report, expanding the party — just in a different way.
Rather than engage women or voters of color, the president expanded Republican margins with white, working-class voters, said Mr. Fleischer, a former press secretary for Mr. Bush who has come to embrace Mr. Trump after leaving his ballot blank in 2016.
Sara Fagen, who was the White House political director for Mr. Bush, agreed: “Trumpism is cemented in,” she said. “The base of the party has changed; their priorities are different than where the Romneys and Bushes would have taken the country.”
Mr. Hawley argued that Republicans should embrace the populist energy of their voters by pursuing the breakup of big technology companies, voicing skepticism of free trade and making colleges more accountable for their high tuition costs.
“If the party is going to have a future, it’s got to become the party of working people,” he said.
Texas may provide a preview of these debates. As Democrats continue to make gains in the state and as the coronavirus rages there, moderate Republicans have tried to steer the state closer to the center while conservatives have tried to push Texas further right.
Hard-line Republican legislators, lawyers and activists have sued Gov. Greg Abbott, a Republican, formally censured him and protested mandates like a statewide mask order. Over the summer, the party elected a new chairman, Allen B. West, a former Florida congressman and firebrand conservative.
“The governor has continued to issue executive orders that are anything but conservative,” said Jared Woodfill, a conservative activist and Houston lawyer who has sued Mr. Abbott. “His base has left him completely.”
Democrats face their own divides over whether to use the moment of national crisis to push for far-reaching structural changes on issues like health care, economic inequality and climate change.
Like Republicans in 2012, Democrats assembled their own task force to try to unify their party after the crowded party primary this year. The group came up with recommendations that were largely broader than what Mr. Biden championed in his primary bid but that stopped short of embracing key progressive policies like “Medicare for all,” the Green New Deal and a fracking ban.
Representative Pramila Jayapal of Washington, a co-chair of the House Progressive Caucus and an ally of Senator Bernie Sanders, said those plans were the “floor, not the ceiling” of what the liberal wing of the party plans to demand should Mr. Biden win. A White House victory, she argued, would give Mr. Biden a mandate to push for more sweeping overhauls.
In Texas, a rising number of young, liberal politicians believe they can finally turn the conservative state blue by embracing a progressive platform.
Two years ago, Julie Oliver lost a House race in Texas’ 25th Congressional District, based in suburban Austin, by nine percentage points — a far closer margin than the 20 points that Representative Roger Williams, a Republican, won by in 2016. This year, the race may be even tighter.
“The things we are talking about two years ago that seemed radical don’t seem so radical today,” said Ms. Oliver, who was endorsed by Mr. Biden last month. “Universal health care doesn’t seem radical. Universal basic income doesn’t seem so radical. These are popular ideas.”
Others in the state worry that their colleagues are forgetting the lessons of recent history. In 2008, Democrats won control of Congress and the White House. But after passing the Affordable Care Act and pushing a climate bill through the House, they lost seats during the midterm elections and their majority in the House.
“We got to remember, midterms are coming,” said Representative Henry Cuellar, a moderate Democrat from South Texas. “If liberals had a mandate, then Bernie Sanders or Elizabeth Warren would have won the primary. The mandate of the American public was to have somebody more to the center.”
Yet in an increasingly polarized country, that center may be shifting.
As he waited for Mr. Cornyn to address the crowd in Plano, Mark Wurst said he had come to embrace the Trump brand of conservatism.
A lifelong Republican, Mr. Wurst, 74, volunteered at the George W. Bush Presidential Library for years. He was skeptical of Mr. Trump initially but was impressed with his actions on immigration and trade — policies that diverged drastically from Mr. Bush’s approach.
“I didn’t know at the time how much I really disagreed with Bush on some things,” Mr. Wurst said. “Look at what Mr. Trump has gotten done. I don’t like his tone, but sometimes you have to look at results.”