The St. Louis Cardinals are in the thick of the playoff race as the MLB season enters its second half. The Cardinals are in a dogfight with the Milwaukee Brewers for the NL Central lead. They currently hold the NL's final wild card spot, but teams such as the Philadelphia Phillies and San Francisco Giants are within striking distance.

St. Louis wants to maximize its playoff chances before the trade deadline on Tuesday. No other move would help them more than acquiring Washington Nationals star Juan Soto. Fortunately for the Cardinals, they are in the thick of trade discussions for Soto.

Soto is one of baseball's brightest young stars. He finished top 10 in NL MVP voting in each of the last three seasons, including second last year. Soto played a key role in Washington's 2019 World Series run with five home runs and 14 RBIs in the postseason.

He recently entered trade talks after rejecting a 15-year, $440 million extension from the Nationals. Many teams are in on Soto, but the Cardinals appear to be one of the frontrunners to acquire him.

St. Louis has the right combination of players and prospects to make a deal work, but they have to be careful. There are some players that should be untouchable in any potential trade.

2 Cardinals players who must be untouchable in Juan Soto trade

2. Jordan Walker

The Cardinals can make a big splash in trade if they want to. They traded for Nolan Arenado and Paul Goldschmidt, two key players on their roster today. However, that's not the way they prefer to build their roster.

St. Louis prefers to build from within and develop its prospects into major league stars. Homegrown players such as Albert Pujols and Yadier Molina are key to the Cardinals' success this century.

Soto is undeniably a special player, but should the Cardinals change their entire philosophy to get him? That's up for debate, but the one prospect they shouldn't even consider giving up is Jordan Walker.

The 20-year-old third baseman is the sixth-best prospect in the entire league, according to MLB.com. In 76 games in AA this season, Walker has 90 hits and 63 runs with a .304 batting average. Additionally, he still has plenty of room to grow as he works his way up the Cardinals' system.

As enticing as Soto is, St. Louis shouldn't mortgage its entire future to acquire him. Giving up Walker would be a big mistake for the Cardinals.

1. Paul Goldschmidt

Goldschmidt, a seven-time All-Star, is still going strong at age 34. The first baseman is top three in baseball in runs, hits and batting average this season. Goldschmidt is currently the betting favorite to win his first NL MVP.

St. Louis has Goldschmidt signed for the next two seasons at $26 million per season. Soto costs less right now at just $17.1 million, but his contract expires after this season. Considering he rejected a deal that would have paid him almost $30 million annually, he will command a big payday this offseason.

The Cardinals would be taking a massive risk by including Goldschmidt in a Soto deal. They'd be giving the Nationals a perennial MVP candidate no matter what, but Soto could walk after this season and leave them with nothing in return.

Giving up a player like Goldschmidt is already a mistake. Add in both players' contract situations, and it potentially becomes a catastrophic mistake.