U.S. Special Counsel Robert Mueller makes a statement on his investigation into Russian interference in the 2016 U.S. presidential election at the Justice Department in Washington, May 29, 2019.
FILE - U.S. Special Counsel Robert Mueller makes a statement on his investigation into Russian interference in the 2016 U.S. presidential election at the Justice Department in Washington, May 29, 2019.

Democrats in the U.S. House and Senate are expected to issue a call Tuesday for Republicans to join in passing legislation to improve election security.

The move comes a day ahead of special counsel Robert Mueller's testimony to two House committees Wednesday about Russia's interference in the 2016 election.

Democrats plan to highlight several House-passed bills and Senate proposals in increased security ahead of the next national elections in 2020.

Congressional Democrats and Republicans remain at odds over how to address election security issues three years after Russia's interference. 

Last month, the Democratic-controlled House passed a bill requiring paper ballots at all polling stations. However, almost all House Republicans opposed the measure, arguing that paper ballots are more susceptible to tampering.

Several Republican-controlled Senate committees have been looking into election security issues, and the Judiciary Committee approved two election security bills in May. However, Senate Democrats accuse Republican leadership of blocking votes on the measures.

Election security has become highly politicized following the Mueller investigation, with both parties disagreeing over how to interpret the report's conclusions into Russia's  interference. 
 
Democrats are hoping to highlight the issue ahead of Mueller's anticipated appearance before two House committees. 
 
Mueller has said he will not offer opinions in his congressional testimony beyond what is in the report, which concluded that Trump had not colluded with Russia to help him win the election, even though his campaign had numerous contacts with Russia.

Mueller reached no conclusion about whether Trump obstructed justice by trying to thwart the investigation, in part because of a Justice Department policy prohibiting charges against sitting U.S. presidents. However, Attorney General William Barr and then-Deputy Attorney General Rod Rosenstein concluded that no criminal charges were warranted against Trump. 

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