When Rep. Mo Brooks was explaining his objections to a House border security bill last week, he paused to check his notes. For reference, he turned to a news release from a fellow Alabama Republican.

“I follow the lead of Sen. Jeff Sessions on that one,” he said.

In the 19 months since the Senate passed a sweeping, bipartisan immigration bill, Mr. Sessions’s dogged opposition has rallied House Republicans to block all but the most conservative immigration measures.

Through meetings with House lawmakers and a prodigious output of written materials, Mr. Sessions has made the rare leap across the Capitol, where GOP lawmakers often eye senators’ attempts to influence them with suspicion.

Mr. Sessions spots a missed opportunity for Republicans.

“Democrats fight with more passion in defense of illegal immigrants than Republicans fight in defense of American workers,” Mr. Sessions wrote in a handbook he circulated this month on the issue.

Now Mr. Sessions’s opposition to a House border-security bill scheduled for a vote this week will spotlight, and test, his efforts to rally conservatives to his side. The measure was one of the few changes to the immigration system where Republicans had been expected to agree, and Mr. Sessions’s efforts are prompting criticism from backers of the House bill.

“For God’s sake, if we can’t unite around border security, what can we unite around?” said Michael McCaul (R., Texas), chairman of the House Committee on Homeland Security.

Mr. McCaul already had toughened language in a bill his committee produced in 2013, making it more prescriptive with details about equipment and approaches the agency must take in each section of the southern border.

Mr. Sessions, however, opposed Mr. McCaul’s bill. He argued that sending additional resources to the border is fruitless as long as the Obama administration allows some illegal immigrants into the country, and unless there is stricter enforcement of laws for those who already are here.

Mr. McCaul has said some of conservatives’ concerns only can be addressed in the Judiciary Committee, whose chairman, Bob Goodlatte (R., Va.), has promised to address other enforcement issues in coming legislation.

Moreover, some conservatives are concerned that the Senate could seek to redirect attention to the border bill, rather than previously passed House legislation seeking to block implementation of the president’s executive order on immigration, as it searches for a way to keep the Homeland Security Department funded beyond Feb. 27.

Due to their concerns, some House conservatives are trying to delay a Wednesday vote on the border bill, GOP aides said.

Whether Mr. Sessions has built enough momentum to derail the House bill this time remains to be seen. Many lawmakers say they are still undecided, and House GOP aides expect the measure to pass.

Nevertheless, Mr. Sessions’s continued involvement reflects his rise as one of Washington’s most prominent critics of the nation’s immigration system.

Last week he was named chairman of the Judiciary Committee’s immigration subcommittee. His staff now tweets from the @ImmigrationGOP handle.

Earlier this month, Mr. Sessions released his 25-page “immigration handbook,” which details his case against both illegal and in some cases legal immigration, arguing that an influx of low-wage workers depresses wages and job prospects for U.S. citizens.

Mr. Sessions is up against supporters of increased immigration—including some in his own party—who say that immigrants often fill jobs that U.S. workers won’t accept and help fuel innovation.

“Some of the points we raised have resulted in improving the legislation,” Mr. Sessions said, referring to his involvement in a bill last summer dealing with the surge of young migrants on the southern border. Encouraged by Mr. Sessions, conservatives raised objections that forced GOP leaders to pull the measure from the floor and change it to appease them.

Mr. Sessions isn’t the only senator who has built a following among House Republicans. Sen. Ted Cruz (R., Texas) often has met with House colleagues, most prominently during the fight about health-care funding that helped lead to the 2013 partial government shutdown.

Mr. Sessions’s arguments have been convincing to some conservative House Republicans.

“It does not secure the border,” freshman Rep. Dave Brat (R., Va.) said of the McCaul bill on a local radio show last week. “I agree with Sessions on about everything he says when it comes to this issue.”

Some House members, however, believe Mr. Sessions is meddling.

Rep. Luis Gutierrez (D., Ill.), a leading supporter of liberalizing immigration law, said Republicans would have trouble expanding their appeal among voters by tapping Mr. Sessions for a more prominent immigration role. “I don’t think Sessions is going to lead them there,” Mr. Gutierrez said on MSNBC on Friday.

Frank Sharry, who leads the immigration advocacy group America’s Voice, said Mr. Sessions’s focus on increasing deportations above all else is bad policy and damaging politics for the GOP.

“Republicans will rue the day they handed the keys to the car to Sessions,” he said. “He is intent on moving the center of gravity on immigration within the GOP far to the right, and…seems to be succeeding.”

Centrist Republicans say they are eager to pass the border bill and move on to fixing other parts of the immigration system after two years of inaction on the issue.

“I’m just tired of defending nothing,” said Rep. Mark Amodei (R., Nev.) “OK, you wanted border [legislation] first, here you go. Let’s turn the page and get onto the other stuff.”

The McCaul bill would provide $10 billion for equipment and technology along the southwest border, including an array of drones, surveillance systems for land and sea, radar and fencing.

It would require the government to achieve “operational control” of high-traffic areas within two years, and of the entire southern border within five years. The measure defines control as preventing all unlawful entries, a higher standard than the 90% set out by the same committee in 2013. At the time, Mr. McCaul called 100% control “impossible to achieve.”

The bill cleared the panel last week on a party-line vote.

http://www.wsj.com/articles/senator-presses-both-chambers-on-immigration-1422241819