Five things to know about the lawsuit against the Trump Foundation

New York Attorney General Barbara Underwood's (D) lawsuit against President TrumpDonald John TrumpTrump says he doesn't want to use 'adversary' to describe Russia Comey urges Americans to vote for Democrats in midterms Roby wins Alabama GOP runoff, overcoming blowback from Trump criticism MORE and the Donald J. Trump Foundation landed Thursday after a lengthy investigation into the charity, alleging that Trump violated both federal and state law and setting up another legal battle for the president.

The 41-page petition includes allegations that Trump illegally used the foundation to support his presidential campaign. The charges of improper use go back to Trump's conduct as a private citizen. Three of Trump's adult children, who serve on the board of the foundation, were also named in the lawsuit.

Trump quickly fired back at the legal challenge when it was filed Thursday, vowing to not settle the case.

Here are five things to know from the lawsuit.

Trump's children are involved

The lawsuit doesn’t just target Trump — three of his children, Ivanka, Eric and Donald Trump Jr.Donald (Don) John TrumpGovernment paid K to Trump company for Scotland stay Juan Williams: Putin wins as GOP spins Trump Jr. mocks the 'resistance' over 'baby blimp' in London MORE, who make up the three other members of the Trump Foundation’s board of directors — also face allegations of wrongdoing.

Notable is what the lawsuit alleges they didn’t do: The complaint states that the board didn’t hold a formal meeting for at least 18 years, from 1999 until 2017, in violation of state law.

The complaint also argues that the Trumps didn’t fulfill their fiduciary and legal responsibilities as members of the board by failing to rein in the foundation's founder — their father.

The inclusion of his children escalates the lawsuit from a legal battle for Trump to a more personal one. A clearly irritated Trump lashed out at the attorney general’s office on Twitter shortly after the lawsuit was filed, calling the office “sleazy New York Democrats” and vowing not to settle the case.

It's another complication for Trump involving campaign finance laws

Then-candidate Trump made headlines in January 2016 when he declined to participate in a presidential debate, instead choosing to hold a fundraiser for veterans’ issues.

However, he faced media scrutiny, notably from The Washington Post, over whether those donations actually made it to any of the charities. Trump eventually disclosed the contributions in May 2016, four months after the event.

The lawsuit alleges that out of the $5.6 million raised during that fundraiser, roughly $2.8 million was shifted to the Trump Foundation. However, the attorney general’s office found that Trump campaign staffers — most notably then-campaign manager Corey LewandowskiCorey R. LewandowskiThe Hill's 12:30 Report — Sponsored by Delta Air Lines — GOP spars with FBI agent at tense hearing Washington big names celebrate launch of Hill.TV The Hill's Morning Report — Trump denigrates NATO allies, floats 4 percent solution MORE — gave instructions on how those funds should be dispersed by the foundation.

The office argues that this means the $2.8 million was an in-kind campaign contribution, noting that Trump also bragged about the donations from the fundraiser on the campaign trail.

The president is no stranger to scrutiny over campaign finance laws: Critics have claimed that he may have violated regulations after Trump acknowledged he reimbursed his personal attorney Michael Cohen, who made a payment to adult-film star Stormy Daniels, allegedly to stay quiet about her claims of a 2006 affair with Trump.

However, Cohen, the president and Trump's lawyer Rudy Giuliani have all stated that the payment did not violate campaign finance laws.

The Washington Post reported earlier this year that Cohen is under investigation for campaign finance law violations.

It's a New York feud

The investigation into the Trump Foundation was launched under former New York Attorney General Eric Schneiderman (D), who abruptly resigned from the job earlier this year after allegations of abuse.

Trump had repeatedly targeted Schneiderman long before his campaign and presidency, first going after him on Twitter in 2013 and continuing to do so in the years since.

The former attorney general filed a lawsuit against Trump University that same year, alleging the company engaged in illegal business practices and made false claims to consumers. Trump agreed to settle the lawsuit, as well as two others filed over the company, in November 2016, just days after he won the presidential election.

Trump's legal battles with Schneiderman continued into his presidency, with the former attorney general repeatedly suing the administration and often taking the lead in lawsuits from several states.

Trump also invoked Schneiderman in his tweets over the lawsuit filed Thursday, calling him “disgraced” and “run out of town.” It’s a sign that Trump’s feud with the former official still lingers, even if he’s no longer in office.

It brings more attention to Trump's businesses

This lawsuit thrusts Trump’s personal charity into the limelight, hitting close to home for the real estate mogul.

Trump has kept his personal businesses and charities relatively close since taking office: He largely broke with the advice of ethics experts when he handed over control of the Trump Organization to his sons, Eric TrumpEric Frederick TrumpDem lawmaker calls on House to subpoena American translator from Trump-Putin meeting Government paid K to Trump company for Scotland stay CREW: Trump using visit to Scotland as ‘infomercial’ for golf club MORE and Donald Trump Jr., instead of selling his assets and placing the profits in a blind trust.

The president has also said that special counsel Robert MuellerRobert Swan MuellerSasse: US should applaud choice of Mueller to lead Russia probe MORE looking into his private businesses would cross a red line, and has previously warned him against investigating his family finances in the course of the probe into Russia's election interference.

But this complaint raises questions about practices within Trump’s charity, as well as the president's own use of the foundation. The lawsuit alleges that the then-private citizen ordered money from the foundation be used to settle legal disputes involving his Mar-a-Lago estate and one of his golf clubs, shining more light on how the president apparently used to run his personal affairs.

There's a risk of the lawsuit expanding

Underwood also referred the case to the Federal Election Commission and Internal Revenue Service, arguing that the agencies should examine the foundation for possible violations of federal election and tax laws.

That means that the current state investigation into the charity could expand to the federal level — and Trump’s own administration could be examining the president and his charity.

Trump is already facing pressure from Mueller’s probe into Russia's election interference, as well as several other legal headaches. Another federal probe — this one featuring his businesses and children — likely isn't welcome.

And if the president fulfills his promise to not settle the case out of court, more information about Trump and his foundation could be revealed during the legal battle.