Democrats Nathan Johnson and Beverly Powell defeat state Sens. Don Huffines and Konni Burton in Texas midterm

Republicans' grip on Texas' upper chamber loosened a bit Tuesday night after Democrats picked up two Republican-held state Senate seats.

State Sen. Don Huffines of Dallas was behind Nathan Johnson by 8 percentage points with 100 percent of precincts reporting, and state Sen. Konni Burton of Colleyville was trailing Beverly Powell by 4 percentage points with 100 percent of precincts reporting.

Most of the 15 Texas Senate races on the ballot this cycle were not considered competitive, but recent voting history in three Republican-held districts has put them in play for Democrats. Burton and Huffines were two of three Republican senators in districts where more voters backed Democrat Hillary Clinton over Republican Donald Trump in 2016 or where the president had a narrow winning margin.

The third seat is held by state Sen. Joan Huffman of Houston, who was leading Democrat Rita Lucido by 5 percentage points early Wednesday with all districts reporting.

“I’m feeling really excited about going to Austin with a much better legislative environment,” Johnson, a political newcomer, told The Texas Tribune on Tuesday night. “Everything we tried to do and hope would happen, happened. We had a surge of turnout in disillusioned Democrats and success with winning moderate Republicans. I think that’s what put us over.”

In a concession statement posted to Twitter, Huffines pledged "to work with Mr. Johnson on a smooth transition to best serve the people of Senate District 16.” He added that he would “keep working for common sense conservative solutions that Texans deserve.”

At stake Tuesday was Republicans’ three-fifths majority in the Senate. For years, the GOP faced hurdles to passing some conservative measures out of the upper chamber due to its "two-thirds rule," which required the support of 21 members to bring a bill to the Senate floor. With 20 Republicans in the Texas Senate, that left Republicans one short of moving out bills without the help of a single Democrat.

In 2015, Lt. Gov. Dan Patrick successfully spearheaded a move that lowered the threshold to three-fifths, which allowed the 21 Republicans in the Senate to unilaterally dictate the flow of legislation — and block Democrats’ bills — during the 2015 and 2017 legislative sessions. After tonight's election, there's a 19-to-12 member split in the Texas Senate, meaning Republicans have just enough members to pass legislation without the support of a single Democrat.

While a pickup of two state Senate seats only chips away at the Republican's majority in the chamber, it also loosens Patrick’s grip on the state’s upper chamber, politicos say. That's because Republican senators might have to work across the aisle to get their legislation passed if any member of their caucus opposes a bill.

Working to the GOP’s advantage this year is the recent pickup of Senate District 19, a typically Democratic-friendly seat that Republican Pete Flores won in September. And questions remain on the seat vacated by state Sen. Sylvia Garcia, D-Houston, who won her congressional bid tonight. A dispute over a letter she sent to Gov. Greg Abbott stating her “intent to resign” has stalled a special election to replace her. The issue has yet to be resolved but could ultimately lead to Abbott delaying the special election to replace Garcia long enough that her seat is empty at the start of next session in January.

With two fresh Democratic faces headed to the state Senate in 2019, members of the minority party will still need the support of at least one Republican willing to go against Patrick to overcome the "three-fifths" rule.

Whether such members exist is yet to be seen. And some politicos are skeptical.

“The Texas GOP Senate supermajority is safe — but only barely — and only due to Flores’ upset,” said Mark Jones, a political science professor at Rice University. “That seat, which Republicans Greg Abbott and Dan Patrick had the foresight to see the potential flip, and Texas Democrats inexplicably let fall through their fingers, proved to be decisive to Dan Patrick’s ability to retain his 19-seat supermajority.”

Disclosure: Rice University has been a financial supporter of The Texas Tribune, a nonprofit, nonpartisan news organization that is funded in part by donations from members, foundations and corporate sponsors. Financial supporters play no role in the Tribune's journalism. Find a complete list of them here.