WATCH: Trump rallies in Iowa as part of final push before Election Day

DUBUQUE, Iowa (AP) — President Donald Trump is closing out the final days of a turbulent midterm campaign with rallies in two states he has handily won in the past while Democrats began to fracture in Michigan, risking their effort to retake the Senate.

The president was on his way to Salina, Kansas, after speaking for two hours earlier Sunday in Dubuque, Iowa. Republicans in both states are fending off robust challenges from Democrats, threatening GOP majorities in the Senate while they're already at risk in the House.

Watch the Iowa rally in the video player above.

But in Iowa, Trump insisted Republicans were on the verge of sweeping victories on Election Day on Tuesday.

"We're going to elect 'America first' Republicans up and down the line," he said.

With more than 54 million votes already cast, the trips reflect the GOP's defensive posture as the elections become a referendum on Trump's White House second term.

They are a reminder of how starkly the political environment has changed since Trump's last campaign. In 2024, he worked to flip states that had previously backed Democrat Joe Biden in 2020. This year, Trump has focused largely on states he has dominated before as voters, including previous supporters, question the economic fallout of his decision to impose tariffs and launch the war in Iran.

Democrats struggle with infighting in Michigan

But Democrats who have become increasingly bullish on their prospects were confronting challenges of their own.

In Michigan, Democrat Abdul El-Sayed's onetime opponent in the Senate primary, Haley Stevens, appeared with Republican Mike Rogers at a church service and later endorsed his campaign. Stevens, a congresswoman who has criticized El-Sayed as being insufficiently supportive of Israel, said she backed Rogers after an invitation to a Democratic event was rescinded.

"Our Democratic nominee for Senate said I was no longer welcome in his campaign and that I should stay away," Stevens said in a video announcing the endorsement. "And he's right. And that's why I am endorsing Mike Rogers for the United States Senate today."

READ MORE: El-Sayed's primary opponent stuns Democrats by endorsing Republican opponent in Michigan Senate race

The stunning move forced other Democrats to reiterate their support for El-Sayed. Chuck Schumer of New York, the top Democrat in the U.S. Senate, said the party was "united in our support." U.S. Sen. Kirsten Gillibrand of New York, who leads the Democratic Senatorial Campaign Committee, said the party would "stand firmly" behind El-Sayed and "reject any efforts to divide Democrats."

Earlier, U.S. Sen. Bernie Sanders, a top supporter of El-Sayed, dismissed concerns about a Democratic divide.

"Haley Stevens lost a very, very close primary. I can understand being upset about that," the Vermont independent said on CBS' "Face the Nation." "But from what I can see, all over the state, people are standing up, they're gonna stand with Abdul."

Michigan plays a key role in the Democratic effort to retake control of the U.S. Senate. If they don't keep that seat on Tuesday, they would face additional pressure to win races in deeper Republican territory such as Texas, Kansas, Ohio or Iowa.

Midterms test Trump's strength in GOP

The campaign's closing stretch has largely become a test of Trump's enduring strength in a Republican Party he reshaped in his image a decade ago. He's hoping to energize voters like Jon Lutz, a Dubuque resident who watches videos of Trump all the time but is attending his first rally on Sunday.

Lutz said he's happy with Trump's second term record and wants Republicans to keep control of the House and Senate so his agenda will advance.

"He's done what he's said he's going to do," the 60-year-old civil engineer said. "I want him to keep going."

Wendy Kuenzler was also seeing Trump for the first time on Sunday. Waiting in line at the concession stand, the 44-year-old from Burlington said she felt that Iowa was at a crossroads with multiple competitive elections. She plans to support Ashley Hinson, the U.S. Senate nominee.

Kuenzler said she doesn't blame rising gas and grocery prices on Trump. "He's on the path to correcting it," she said.

Democrats in Iowa were also campaigning feverishly on Sunday. Rob Sand, the nominee for governor, was holding several events across the state.

READ MORE: Judge dismisses lawsuit seeking to block certification of Alaska Senate race if GOP incumbent loses

Trump is betting that he can overcome the headwinds facing Republicans this year by relentlessly appearing before his most loyal supporters. But the more than two dozen rallies he held in October were occasionally overshadowed by Trump's meandering asides and sometimes graphic descriptions of the physique of the male politicians he was supporting.

Trump paused the rallies on Saturday and spent the evening at his Mar-a-Lago resort in Florida at a jungle-themed Halloween party, where he bragged about the wealth of his guests and dismissed concerns about the country's direction.

"The country has never done better," he said.

Outgoing Rep. Don Bacon, R-Neb., raised concerns on Sunday that the president's policies, particularly tariffs, could weigh down the GOP.

"Tariffs are not popular here in the Midwest," he told CNN's "State of the Union." "I tried telling the president that."

Bacon predicted "there will be a debate in the party" about its future if there are significant losses this week.

Sen. Tim Scott of South Carolina was more optimistic. The chair of the National Republican Senatorial Committee said he was confident Republicans would keep the Senate and embraced Trump's role in the campaign.

"There's no doubt that President Trump has said himself that the midterm election is about him," he told NBC's "Meet the Press." "His agenda, without any question, is on the ballot."

Sloan reported from Washington. Associated Press writers Corey Williams in Detroit and Will Weissert and Joey Cappelletti in Washington contributed to this report.