Trump has never condemned Russia over its meddling in the 2016 elections despite the findings of all top U.S. intelligence agencies. In the past, Trump has reiterated Putin’s denials, but this week said he would bring up the issue when the two meet Monday in Finland.

“All I can do is say, ‘Did you?'” Trump said last week at a news conference in Brussels. “And, ‘Don’t do it again.’ But he may deny it.”

Some of the state officials who run elections say it’s important for the president to take a tougher stance to avoid having the public’s confidence in fair elections undermined.

“I believe as commander in chief, he has an obligation to address it, and frankly put Putin and any other foreign nation that seeks to undermine our democracy on notice that the actions will not be tolerated,” California Secretary of State Alex Padilla, a Democrat, said in an interview this week.

Trump portrays the investigation as a partisan attack, but not all Republicans see it that way. This month, the Republicans and Democrats on the U.S. Senate Intelligence Committee backed the findings of an assessment from U.S. intelligence agencies that Russia tried to interfere in the 2016 election — and acted in favor of Trump and against Democratic Hillary Clinton.

As part of that effort, Russian hackers targeted at least 21 states ahead of the election and are believed to have breached the voter registration system in at least one, Illinois. Without naming the state, Friday’s indictment says the Russian intelligence officers stole information on about 500,000 voters from the website of one board of elections, a breach that went undetected for three weeks.

There is no evidence they altered any results, but the attempts prompted the federal government and states to re-examine election systems and tighten their cybersecurity.

Federal officials also say it’s possible that malware might have been planted that could tamper with voting or paralyze computer systems in future elections.

During a hearing this past week, U.S. Rep. Michael McCaul of Texas called the 2016 election meddling “a provocative attack against our country, and we must not allow it to happen again.” McCaul, a Republican who serves as chairman of the House Homeland Security Committee, said he believes the country will be targeted again during the midterm elections in November.

“We need to be prepared,” he said.

On Friday, a federal grand jury indicted 12 Russian intelligence officers on charges that they hacked into Democratic campaign networks in 2016, then stole and released tens of thousands of documents.

The indictment says one of the intrusions came that summer, on a vendor whose software is used to verify voter registration information. The indictment references a spoof email it says the Russian agents sent to more than 100 election-managing customers of the vendor to try to get more information.

“The indictments tell us that … no longer can we deny in any shape or form that Russians were involved,” said cybersecurity expert Sam Woolley of the Institute for the Future in Palo Alto, California.

He said state election officials need to ensure they have the most robust possible protections for their voting systems.

“Right now, this is definitely not the case,” he said. “Most people operate on machines that are not very secure.”

Washington Secretary of State Kim Wyman is scheduled to tell her peers this weekend about how her state is using its National Guard to help test and shore up cybersecurity for elections. She said it’s important to make it clear to voters that the military is not running elections and does not have access to election data.

“We’re acutely aware of the optics of working with the National Guard,” Wyman, a Republican, said in an interview. “The whole idea of this is to instill confidence in voters and the public that the system is secure.”

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Associated Press writer Angela Charlton in Paris contributed to this report.