Rep. Jefferson Van Drew (N.J.) has drawn his first Democratic challenger since moving over the weekend to switch political parties and become a Republican.

Brigid Harrison, a political science professor at Montclair State University, announced on Monday that she would run to unseat Van Drew from his southern New Jersey congressional district in 2020 after he told aides that he planned to become a Republican following a White House meeting with President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE.

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“Jeff Van Drew Jeff Van DrewThe Hill's Campaign Report: 19 years since 9/11 | Dem rival to Marjorie Taylor Greene drops out | Collin Peterson faces fight of his career | Court delivers blow to ex-felon voting rights in Florida The Hill's 12:30 Report: First Kennedy to lose a Massachusetts election Ex-Democrat Van Drew speaks at GOP convention MORE made a choice,” Harrison said in a statement sent to reporters. “He has repeatedly ignored the voices of our community and has instead sold his soul, cutting backroom deals with the White House.”

“Whether you are a Democrat, Republican, or Independent, the last thing the people of the 2nd Congressional District need or want is to elect a blind pawn for Donald Trump.”

Van Drew, a moderate who was among the Democratic Party’s most vocal opponents of ongoing impeachment proceedings against Trump, flipped New Jersey’s Republican-held 2nd District in 2018. Trump won the district in 2016 by just under 5 percentage points.

Even before news of his planned party switch broke over the weekend, Van Drew was expected to oppose Trump’s impeachment, prompting chatter that he could face a primary from his left in 2020.

Van Drew’s decision to switch parties amid the impeachment proceedings underscores the political pressure faced by first-term Democrats who helped flip Republican-leaning districts in last year’s midterm elections. Many of those members won in districts that Trump carried in 2016.

But Van Drew’s decision carries risks, as well. Democrats have already accused him of selling out his values and his party in order to buoy his reelection prospects in 2020. And seven of his aides in Washington resigned over the weekend, saying that his “decision to join the ranks of the Republican Party led by Donald Trump does not align with the values we brought to this job when we joined his office.”

Sen. Cory Booker Cory Anthony BookerSunday shows preview: Lawmakers prepare for SCOTUS confirmation hearings before election The movement to reform animal agriculture has reached a tipping point Watchdog confirms State Dept. canceled award for journalist who criticized Trump MORE (D-N.J.), one of the state’s two Democratic senators and a presidential candidate, called earlier on Monday for his supporters to mobilize against Van Drew and donate to a fund supporting his eventual Democratic challenger.

Harrison appears likely to seize on Van Drew’s party switch in her campaign. The topic is front and center on her campaign website.

“When Jeff Van Drew went to Washington, the first thing he did was take an oath to ‘support and defend the Constitution of the United States against all enemies, foreign and domestic,’ ” a post on her website reads. “But Congressman Van Drew’s actions make it clear he is putting his own political interests ahead of his oath to the Constitution and those who elected him in South Jersey.”