CLAYTON, Mo. (AP) — A Missouri congressional race on Tuesday will serve as a test of the inroads Democrats believe they are making in the suburbs.

Four-term incumbent Republican Rep. Ann Wagner is facing a strong challenge from Democratic state Sen. Jill Schupp in Missouri's 2nd District, which covers mostly middle class and affluent parts of the St. Louis suburbs.

Most experts see the race as a toss-up, and both sides have spent heavily, with Wagner's campaign shelling out about $5 million, Schupp's about $4 million and outside groups pouring in millions more in support of one candidate or the other.

The 2nd District hasn't sent a Democrat to Congress since 1990. This year, though, the top of the Republican ticket could hurt Wagner's chances, as polls show a big drop in suburban support for President Donald Trump since 2016, especially among women. That year, he defeated Democrat Hillary Clinton in the district and carried Missouri by nearly 19 percentage points.

Wagner beat her Democratic opponent by 21 percentage points in 2016. But when Democrats captured House control in 2018, many of the 40 seats they gained were in suburban districts, and Wagner's winning margin was cut to 4 points.

Wagner is one of more than a dozen Republican incumbents from suburban areas around the country who are facing strong Democratic challengers.

Schupp said last month that her focus was on Wagner, not Trump. In a separate interview, Wagner touted some of the accomplishments of the Trump administration, such as lowering taxes and cutting regulations. She distanced herself from his personal behavior, saying she has “never felt that I had to personally tear another person down to lift my values, my policies, my beliefs up.”

Schupp has focused largely on health care. Several TV ads cited Wagner's votes to repeal the Affordable Care Act and noted that doing so would remove protections for preexisting conditions for millions of Americans at the worst possible time — during the coronavirus pandemic.

Wagner said she supports two provisions of the ACA, also known as Obamacare — covering preexisting conditions and allowing adult children to stay on their parents’ health insurance plans until age 26.

She pointed to legislation she sponsored that would make protections for preexisting conditions “an absolute fundamental right” enshrined in law, even if the Supreme Court ultimately strikes down the ACA.

Wagner's campaign ads have accused Schupp of being soft on crime. One shows protesters stomping a police car as the narrator accuses Schupp of receiving support from “radical defund the police organizations.”

Advocates for defunding generally mean shifting money from law enforcement to things such as mental health services and crime prevention.

Schupp said she does not support defunding police but does support police reforms.

Wagner, 58, was a top GOP leader in Missouri and served as ambassador to Luxembourg under President George W. Bush before her election to Congress in 2012. Schupp, 65, is a four-term state legislator.