With the March 5 California Senate Primary just weeks away, Congressman Adam Schiff appears to be succeeding in his strategy of boosting the Republican nominee, baseball star Steve Garvey, to box out other Democrats from the November ballot.

A new survey from Emerson College Polling, Inside California Politics, and the Hill finds that Mr. Schiff is leading the pack with 28 percent support in the Senate primary.

In California, primaries are nonpartisan affairs, where every candidate runs against one another, and the top two vote-getters from the primary advance to the general election.

The survey also found that Mr. Garvey is polling in second place with 22 percent support. Congresswoman Katie Porter was the third most popular candidate, polling at 16 percent, and Congresswoman Barbara Lee enjoyed 9 percent support.

Mr. Schiff has invested significant resources into boosting Mr. Garvey in order to avoid facing another Democrat in the general election.

A political scientist at John Jay College, Brian Arbour, tells the Sun that Mr. Schiff, who has the backing of Democratic leaders like Speaker Pelosi, would be nearly guaranteed to win if he faces off against Mr. Garvey.

“If the general election is between a Democrat and a Republican, then the Democrat will win easily. So Schiff wants the race to be between him and Garvey,” Mr. Arbour says.  “If the race is between Schiff and one of the other Democrats, then it’s much more unpredictable who will win.”

The political spending watchdog AdImpact reports that Mr. Schiff has invested in a $9.6 million ad campaign to close out the primary. Ms. Porter is expected to spend only about $3 million. From a new ad released Tuesday, it’s clear that at least some of Mr. Schiff’s spending will be aimed at boosting Mr. Garvey.

“Democrats agree, conservative Republican Steve Garvey is the wrong choice for the Senate,” the ad says in its opening, before cutting to footage of Ms. Lee saying “Our Republican opponent here on this stage has voted for Donald Trump twice.”

The ad continues “Garvey is wrong for California, but Garvey is surging in the polls. Fox News says Garvey would be a boost to Republican control of the Senate.” 

The latest round of spending is only a fraction of the total that Democrats have invested into the primary so far. AdImpact reports that Democratic candidates and groups have invested some $32.8 million into the race. Republicans have only spent around $18,000.

Broken down by candidate, however, Mr. Schiff is far and away the biggest spender in the race, with some $21.5 million being spent to support his candidacy, about $10 million being spent to support Ms. Porter, and just about $1.3 million being spent to support Ms Lee.

While $32.8 million represents a significant expenditure for candidates and Democratically affiliated organizations, it could save money in the long run. If the party can engineer a Mr. Schiff versus Mr. Garvey matchup in the general election, it could avoid an expensive intraparty battle between two Democrats in November.

There are some indications that Ms. Porter may have a leg up against Mr. Schiff in a head-to-head matchup, with a survey commissioned by Ms. Porter’s campaign and conducted late last year by David Binder Research finding that Ms. Porter led Mr. Schiff 37 percent to 26 percent when no other candidates were in the race.

The Emerson College Polling survey of 1,000 registered was conducted between February 16 and 19 and had a credibility interval of plus or minus 3.1 points.