Indiana Senate Republicans failed to pass a redistricting bill that would have edged out the state's two House Democrats, despite months of pressure from the Trump administration and after state senators faced bomb and swatting threats.

The final vote was 19 senators in favor and 31 against. Republicans have 40 seats in the state Senate to Democrats' 10. 

Thursday's failure marks the first time national Republicans' redistricting plans have been thwarted since the push to redraw congressional maps was kicked off by President Trump over the summer. 

Republican Gov. Mike Braun, who supported redistricting, posted on social media that he is "disappointed" in the result, and said he will be "working with the President to challenge these people who do not represent the best interests of Hoosiers."

Mr. Trump has vowed to back primary challenges against Republicans who voted against the Indiana measure, and took aim on Wednesday at Senate president pro tempore Rodric Bray. 

"Anybody that votes against Redistricting, and the SUCCESS of the Republican Party in D.C., will be, I am sure, met with a MAGA Primary in the Spring," Mr. Trump posted on social media ahead of the vote. "Rod Bray and his friends won't be in Politics for long, and I will do everything within my power to make sure that they will not hurt the Republican Party, and our Country, again."

As the state Senate debated the vote, Vice President JD Vance posted on social media that Bray "consistently told us he wouldn't fight redistricting while simultaneously whipping his members against it. That level of dishonesty cannot be rewarded, and the Indiana GOP needs to choose a side." 

There were several hours of impassioned debate on Thursday from senators both in favor of and against redistricting. 

"I, like a supermajority of you, do not want to see another Democrat Speaker of the House," said Republican state Sen. Spencer Deery, who opposed redistricting. "But that isn't for me to decide, and it isn't for anyone in this body to decide either. Living in a free constitutional republic means we empower voters to make those decisions."

Indiana, which Mr. Trump won last year by 19 points, was among several Republican-led states under pressure from the president and his allies to redraw its maps. Its House delegation is 7-2, with Democrats holding one seat that encompasses Indianapolis and another in the southwestern corner of the state. 

In November, Gov. Mike Braun called the legislature to reconvene for a special session to consider redistricting. But Bray insisted that the votes weren't there, and when the legislature convened, state lawmakers simply agreed to meet again in January for the regular session. 

Although Republicans hold 40 seats in the state Senate and needed only 25 votes to pass the legislation, Bray expressed doubt that there was enough support to pass the new maps.

After the November session, Mr. Trump stepped up his social media posts about the Indiana vote. State lawmakers began receiving bomb threats and swatting attacks. The Indiana state police said last week that "numerous" members of the State Assembly had received bomb threats and were victims of swatting hoaxes. Braun confirmed that he had also received threats. 

Indiana's House and Senate GOP leaders announced before Thanksgiving that they would return to vote on redistricting. The measure passed the House, but Bray remained uncertain if it would pass the Senate. 

On Monday, the elections committee heard public testimony about the new map. According to The Associated Press, 127 people signed up to testify. Just 18 of them backed the bill, while the rest were opposed. 

Republican state Sen. Greg Walker gave an impassioned speech Monday about the threats he had received before voting against advancing the measure. 

"I fear for this institution, I fear for the state of Indiana, and I fear for all states if we allow intimidation and threats to become the norm," Walker said. 

The nationwide redistricting gambit kicked off over the summer, when Texas' GOP-led legislature reconvened to redraw the state's maps to net up to five seats for Republicans. In response, California Gov. Gavin Newsom pushed forward with a ballot measure known as Proposition 50 to redistrict his state to net up to five seats for Democrats, since California requires voter approval of its congressional map. Prop 50 passed on Election Day with more than 64% of the vote.

Missouri and North Carolina's Republican-led legislatures have each redrawn their maps in an attempt to gain a new GOP-friendly seat. 

Maryland Democrats may undertake a similar effort to edge out the state's one Republican House member, though the idea has faced resistance from some Democratic legislators. 

The redistricting campaigns have drawn lawsuits in some states. The Supreme Court last week allowed Texas to use its newly drawn congressional map for now, halting a lower court ruling that found the new map was racially gerrymandered. 

Editor's note: This story was updated to correct an inaccuracy in the number of senators who voted against the bill.