The Republican lawmakers gathered in Baltimore erupted in cheers and laughter Thursday as President Trump warned of “the dangers” of energy-saving lightbulbs and falsely claimed that televisions turn off when wind turbines stop spinning. 

“Mr. President, we are with you the entire way!” House Minority Leader Kevin McCarthy (R-Calif.) said as Trump ended his speech at the House GOP retreat.

 About 1,500 miles away in Houston, former vice president Joe Biden faced accusations of having a faulty memory during an intense Democratic presidential debate that exposed deep ideological divisions and included a few personal swipes.

At one point, Sen. Amy Klobuchar (D-Minn.), urged her fellow Democrats to stop their bickering, warning that “a house divided cannot stand.”

In the third Democratic debate on Sept. 12, the 10 candidates on stage shifted their focus from attacking President Trump to taking shots at one another. (The Washington Post)

Thursday night brought into sharp relief the way America’s two major political parties have been reshaped by Trump. After an unexpected 2016 loss, Democrats have struggled with whether to bolster or restrain the party’s leftward shift. Republicans, meanwhile, have completely ceded the party’s orthodoxy to a president whose views on trade, entitlements and political decorum bear little resemblance to traditional conservatism.

Both approaches carry major risks ahead of next year’s presidential election. Democrats are desperate to unseat an unpopular president but divided about how to do it without alienating chunks of their base. Republicans, meanwhile, have largely coalesced around Trump, but it’s far from clear that the president has a winning message for 2020.

 For both parties, Trump is the main driver of the disruption, said Amy Walter, national editor of the Cook Political Report.

South Carolina, Nevada, Arizona and Kansas have canceled their Republican primaries and caucuses for the 2020 presidential election. (Blair Guild/The Washington Post)

“Democrats are trying to figure out who is the candidate that can play on Trump’s terrain, which is different from any terrain we’ve ever seen in modern politics,” she said. “For Republicans, the ones who have criticized the president have either lost or left. . . . Distancing yourself from the top of the ticket is almost impossible now.”

 The competing trends are in some ways a reflection of a political landscape where a party in power rallies around its standard-bearer while the opposition seeks new strategies as it tries to regroup.

 But, like many things involving Trump, they have been supercharged by a polarizing president who dominates the politics of both parties, Walter said. 

 During Thursday’s debate, several hopefuls used their opening statements to assert that Democrats were mostly united on the major issues of the day and shared the goal of defeating Trump.

But the veneer of unity quickly gave way as the 10 candidates onstage sparred over whether the party should pursue an agenda of transformational change or embrace a more incremental approach.

The debate began with a fierce exchange on health care, an issue that has come to represent a broader struggle within a party riven by ideological and generational fault lines.

 “Nobody’s yet said how much it’s going to cost the taxpayer,” Biden said after a lengthy discussion of the Medicare-for-all idea backed by Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.). 

He called Sanders a “socialist” with unrealistic ideas about how the private sector would respond to his plan.

Julián Castro jumped in and inaccurately accused Biden of changing his position within minutes, alluding to questions about the 76-year-old’s age and mental acuity.

“Are you forgetting what you said two minutes ago?” he said.

“This is why presidential debates are becoming unwatchable,” South Bend, Ind., Mayor Pete Buttigieg said after Castro claimed that he was the rightful bearer of Barack Obama’s legacy, rather than Biden. 

Those fights underscore the deeper identity crisis roiling the party. Concerned that the president could repeat his 2016 performance in key states like Michigan, Wisconsin and Pennsylvania, Democrats are conflicted over whether to focus on converting Trump voters or juicing enthusiasm among Democratic base voters who stayed home in 2016. 

Neither tactic is a sure bet. A Biden campaign makes it harder to engage the party’s leftward flank.

But Warren or Sanders could drive away support among the suburban voters who have been turned off by Trump’s presidency. And both have struggled to connect with nonwhite voters, a core Democratic constituency.

The candidates are also trying to determine how to address the legacy of Obama, a popular Democratic president who nonetheless faced criticism from some liberals over immigration and other issues. 

Biden, who served as Obama’s vice president for eight years, has hewed most closely to the record and policies of the former president. 

“I stand with Barack Obama all eight years, good, bad and indifferent,” Biden said at the debate when challenged over the Obama administration’s record on deportations.

Sanders and Warren have promised broader change than what Obama pursued, arguing that a more ambitious approach is needed to address income inequality and the conditions that gave rise to Trump.

As Democrats debate, Trump has repeatedly celebrated the support he has received from his party. 

“94% Approval Rating in the Republican Party!” Trump tweeted Saturday, repeating a “high and very beautiful number” not backed by public polling. Various polls have put Trump’s approval rating among Republicans at 80 to 90 percent.

 But at the House GOP retreat in Baltimore, the president could easily get the impression of unanimous party support from a caucus that lost its majority in last year’s midterm elections. 

“The Republicans have never been more united,” McCarthy said at one point.

Trump’s takeover of the party was evident throughout the three-day retreat in Baltimore. The schedule included breakout sessions on foreign policy, the military and politics but nothing on reducing the national debt or entitlement reform.

Those once fundamental conservative priorities largely have been left behind in the Trump era. In 2018, Republicans passed a massive tax cut that ballooned the deficit. Then Trump, never keen on big spending cuts, shot down then-speaker Paul D. Ryan’s plea to tackle entitlements.

On Thursday, the Treasury Department reported that the government’s budget deficit had surpassed $1 trillion, with a month left in the fiscal year.

“It used to be the case that establishment Republicans were very attentive to the fiscal situation,” said Mark Zandi, chief economist at Moody’s Analytics. “But there is no political anchor now around fiscal discipline.”

The president has been able to consolidate Republican support by pushing an us-against-them message that many in the party have replicated on the campaign trail.

“With the grim specter of socialism descending on the Democrat party, it’s up to all of us to ensure the survival of American liberty,” Trump said during his speech Thursday. He mocked Buttigieg’s height, described Biden as “sleepy Joe” and referred to Sanders as “crazy.”

Privately, Republicans acknowledge that Trump’s divisiveness has created a problem for them in suburbs. In 2018, Republicans lost 40 seats to Democrats, including 29 incumbents. GOP leaders, now in the minority, had tried to explain to the president that they needed his help stopping the suburban bleeding. 

Highly educated suburban voters are leaving the party, making it harder for Republicans to take back control of the House. At least 17 House Republicans, including the caucus’ only black member, have already announced their intention to retire, resign or seek another office.

But Trump has encountered little public resistance within his party for his scorched-earth political strategy, which has at times included racist language. Republican senators including Ben Sasse of Nebraska and Lindsey O. Graham of South Carolina, both onetime Trump critics facing reelection this year, have either gone silent or transformed into cheerleaders for a president who prizes loyalty.

Trump’s erratic approach to foreign policy and trade has forced the party to abandon many of its core tenets and left an ideological hole that’s often filled by the president’s Twitter account. 

A spat between Rep. Liz Cheney (Wyo.) and Sen. Rand Paul (Ky.) laid bare the internal divisions that persist within the GOP between its hawks and its libertarians. As Trump has vacillated between muscular rhetoric and an “America first” approach to foreign policy, both Cheney and Paul have sought to claim the mantle of Trumpism despite their very different views on foreign policy.

“I’m just grateful for a president who, unlike you, supports stopping these endless wars,” Paul tweeted at Cheney on Thursday.

A day earlier, Cheney tweeted: “I stand with @realDonaldTrump and our men and women in uniform who will never surrender to terrorists, unlike @RandPaul.”

Still, Trump’s campaign says the party will be unified going into 2020 in part because Democrats have moved far to the left. Trump has said publicly that even Republicans who don’t like him “have no choice” but to vote for him. 

Trump’s campaign has worked to stifle any internal challenges to the president’s reelection, working with state party leaders to ensure a smooth path to the GOP nomination for the president. Republican parties in South Carolina, Arizona, Nevada and Kansas have canceled their primaries and caucuses, all but ensuring that Trump will win their states’ delegates. The moves have led to outcry from Trump’s primary challengers.

But the president has made it clear that party unity will be a key part of his political strategy as 2020 approaches.

“And I’ve always said about the Democrats, they’re lousy politicians but they have one thing that’s incredible: They stick together,” Trump told the GOP leaders in Baltimore. “And you people have to stick together. And you do. I know you.”