WASHINGTON -- House Speaker Paul Ryan is jumping into the high-stakes battle over New Jersey congressional seats that can turn from red to blue this fall in President Donald Trump's big midterm test.

House Republicans have gone on the attack to preserve endangered New Jersey representatives Tom MacArthur and Leonard Lance, launching ads against their Democratic challengers.

The TV ads funded by the Congressional Leadership Fund, the super political action committee aligned with Ryan, R-Wis.

They criticize former national security aide Andy Kim and former Assistant U.S. Secretary of State Tom Malinowski, two veterans of President Barack Obama's administration.

Both Kim and Malinowski are no worse than even money to defeat the GOP incumbents, according to the Cook Political Report, and both entered July with more money to spend than their opponents, according to Federal Election Commission reports.

A Monmouth University Poll released earlier this week gave MacArthur, R-3rd Dist., a mere 1-point lead among potential voters over Kim, 41 percent to 40 percent, well within the survey's margin of error of 4.9 percentage points.

In the Congressional Leadership Fund commercial, Kim's campaign is described as being "bankrolled by Nancy Pelosi."

Kim has received $14,000 in contributions from the House Democratic leader's campaign committee and leadership PAC, which is less than 1 percent of the $2.2 million he's raised through June 30, FEC filings show.

The ad targeting Malinowski goes after his support of the multinational agreement that relaxed economic sanctions on Iran in exchange for curbs on its nuclear program. The spot also brands as a "D.C. lobbyist" someone who not been registered for a decade, according to congressional filings, and when he did lobby, he was working for Human Rights Watch, an advocacy group that co-founded the Nobel Peace Prize-winning International Campaign to Ban Landmines.

Both ads criticize the Democrats for opposing the Republican tax legislation, which studies show gives most of its benefits to the wealthy and corporations and targets New Jersey and other high-tax states, most of which send billions of dollars more to Washington than they receive in services..

Just 36 percent of New Jerseyans supported the measure in an April Monmouth poll, with 45 percent opposed.

MacArthur sided with Ryan, House Republican leaders and President Donald Trump in voting to support the tax bill and repeal the Affordable Care Act.

Lance bucked his party and voted against both measures. He represents one of only 23 Republican-held House districts whose voters supported Democrat Hillary Clinton for president in 2016.

The Congressional Leadership Fund earlier set up field offices in MacArthur's and Lance's districts to make phone calls and go door-to-door on behalf of the two incumbents.

The group announced in April that it had reserved $1.4 million in advertising time to help MacArthur and said in June it had set aside $2.1 million for Lance.

The super PAC reported raising $120 million through July 18 for the 2018 midterms.

Four of the five Republican-held districts in New Jersey are up for grabs this fall, with Democrats already favored to win the seats being vacated by retiring Reps. Frank LoBiondo, R-2nd Dist., and Rodney Frelinghuysen, R-11th Dist.

Check out the ads here.

Jonathan D. Salant may be reached at jsalant@njadvancemedia.com. Follow him on Twitter @JDSalant or on Facebook. Find NJ.com Politics on Facebook.